Trees of Angel Island (2-24-24)

I did a bike trip to Angel Island today, not thinking I would see a lot of tree diversity. As expected, the island is full of coast live oaks, toyon and the occasional California buckeye and California bay. But what I didn’t expect was to find some unusual specimen trees near the Angel Island Immigration Museum.

To get to the immigration museum, you head downhill from the Perimeter Road at a point on the northeast part of the island. On the walk down, on your left you’ll see a couple of stately spotted gums (Corymbia maculata).

spotted gums (Corymbia maculata)

Continue down the road to the open area below the museum, and to your far left is a large bunya bunya tree tree (Araucaria bidwillii), native to Australia. Bunya bunyas are rare in San Francisco, and one of our best was just cut down in West Portal at Vicente and Wawona, so this was a welcome sight.

bunya bunya tree (Araucaria bidwillii)


At the other end of the clearing near the museum is a close relative of the bunya bunya - a Norfolk Island pine (Araucaria heterophylla), also large and mature. It wouldn’t surprise me if they were planted at the same time.

Norfolk Island pine (Araucaria heterophylla)

And in between the two Araucaria, facing the water, two Canary Island date palms (Phoenix canariensis).

Canary Island date palms (Phoenix canariensis)

Angel Island used to be full of blue gum eucalyptus trees (Eucalyptus globulus), but 80 acres of eucalyptus were removed in the 1990s - among other things, they were thought to be a fire hazard that created risk for the nearby historic buildings. However, there are still beautiful specimens of this tree to be found around the island.

blue gum eucalyptus (Eucalyptus globulus)

And lastly, the most common tree on the island - coast live oak (Quercus agrifolia).

coast live oak (Quercus agrifolia)

Trees of Mexico City (1-25-24)

I visited Mexico City with my family in late January 2024 - we stayed in the Roma Norte neighborhood, and didn’t stray very far from there, so this blog may not be representative of the entire city’s trees.

It was my first time in Mexico City. I had heard that the city was very leafy, and I found that to be accurate. In fact, at least in the Roma Norte neighborhood, the street trees are so dense that it’s not easy to get an Instagram-worthy photo of an individual tree! This link from Google maps of a street not far from our hotel will give you a sense of this part of Mexico CIty.

We visited one of the city’s botanical gardens (Jardin Botanico del Bosque de Chapultepec), but I found it underwhelming. The cactus and agave collections were attractive, but the park is relatively small (13 acres), and very few tree specimens were labeled.

The three species that dominated the streets of our neighborhood were shamel ash (Fraxinus uhdei), glossy privet (Ligustrum lucidum) and American sweetgum (Liquidambar styraciflua). Two of the three are native to Mexico - shamel ash is native from west-central Mexico to Costa Rica, and sweetgum is found in disjointed areas from central Mexico to Nicaragua.

shamel ash (Fraxinus uhdei)

The ash trees were the most abundant of all, which saddened me a bit to think that the emerald ash borer is marching across the continent, killing every ash it encounters, and eventually I suspect will make it to Mexico City.

shamel ash (Fraxinus uhdei) - closeup of leaves and samaras (fruits)

glossy privet (Ligustrum lucidum) - closeup

American sweetgum (Liquidambar styraciflua) - closeup of leaves

Another tree that was very common on city streets was weeping fig (Ficus benjamina). It’s very rare as a street tree in my native San Francisco, but I saw it everywhere in Mexico City.

weeping fig (Ficus benjamina) - closeup

weeping fig (Ficus benjamina)

Occasionally I ran across orchid trees (Bauhinia purpurea) in bloom as street trees.

orchid tree (Bauhinia purpurea)

Not a tree, but another plant I saw everywhere in our neighorhood was split leaf philodendron (Thaumatophyllum bipinnatifidum).

When we ventured out of Roma Norte into other neighborhoods, the canopy thinned out a bit (and I also started to see some more unusual tree species. Below is a Cook pine that we encountered in the Condesa neighborhhood, not far from the city’s botanical garden. This tree always leans towards the equator (a discovery by botanist Matt Ritter in 2017), and this one was duly leaning south!

Cook pine (Araucaria columnaris) on Calle Juan de la Barrera near the corner of Avenida Mazatlan in the Condesa neighborhood

We visited Casa Gilardi, a home designed by minimalist architect Luis Barragan-designed - the family that has owned it since it was built it gives private tours. It’s in the San Miguel Chapultepec neighborhood, and if you’re into architecture or home design, I really recommend it. Inside the open air courtyard of the home is a large jacaranda (Jacaranda mimosifolia), a tree native to Argentina and Bolivia - but very popular in Mexico City.

the indoor pool at Casa Gilardi

a hallway at Casa Gilardi

jacaranda (Jacaranda mimosifolia) in the courtyard at Casa Gilardi

A couple of days later I saw what I think it the largest jacaranda I’ve ever seen - the address is 208 Jalapa in the Roma Norte neighborhood.

a huge jacaranda (Jacaranda mimosifolia) at 208 Jalapa in Roma Norte

At 7,350 feet in altitude, Mexico City isn’t tropical, but since it rarely has freezing temperatures, there are lots of palm trees that do well here. Canary Island date palms (Phoenix canariensis) were pretty common.

Canary Island date palm (Phoenix canariensis)

And not far from our hotel (at the intersection of Calle Jalapa and Calle Puebla in Roma Norte), we found a corner full of bismarck palms (Bismarckia nobilis), a tree native to Madagascar.

bismarck palm (Bismarckia nobilis)

Compared to my native San Francisco, there were relatively few eucalyptus trees. We did see a beautiful eucalyptus relative - a spotted gym (Corymbia maculata) on Avenida Insurgentes Sur near Avenida Alvaro Obregon in Roma Norte.

spotted gym (Corymbia maculata) - Avenida Insurgentes Sur

Fairmount Hill Tree Tour (2-3-24)

 

 

Between showers on a mostly windless day, we chose a relatively quiet neighborhood wedged between the northeastern extent of Glen Park and the southern extent of Noe Valley. It covers the lower slopes of a hill known as Fairmount, one of the many hills that make up the San Miguel Hills in this part of the city. We were pleased with the diversity of trees in this small neighborhood. But, the real draw is the variety of residential architecture, from stunning and beautifully restored Victorians to modest cottages, along with some ‘50s-‘60s apartment buildings. Laidley Street is known for its collection of radical contemporary architecture from the ‘80s and ‘90s. Take time to appreciate this diversity in residential design. 

Today’s walk is a simple one. It begins on Whitney Street, at its terminus at Chenery Street. It heads north on Whitney for two blocks to Randall Street, then continues on Randall for two more blocks to Harper Street, and heads uphill on Harper to Laidley Street. From there it heads southeast-ish on Laidley to Miguel Street, downhill on Miguel to Whitney, and then north again on Whitney for a few yards. This walk is almost a mile and a half in length.

 Numbered trees are labeled with common and scientific names and country of origin, all written in white chalk on the sidewalk; accompanying numbers, in blue, run from 1 to 34. White arrows on the pavement provide directions whenever a turn is needed. 

Whitney Street, Chenery to Fairmount, east side

1. 298 Chenery            Brisbane box (Lophostemon confertus), E Australia (tree is on Whitney)

 2. 263 Whitney           Cajeput tree (Melaleuca quinquenervia), New Caledonia, New Guinea, E Australia (3 trees, including 1 across the street; feel the distinctive spongy bark)

 3. 249 Whitney           Ginkgo (Ginkgo biloba), China (last of an ancient lineage; there are many ginkgos in the neighborhood, including some very young ones on Miguel)

Chinese elm (Ulmus parvifolia)

 4. 249 Whitney           Chinese elm (Ulmus parvifolia), China, Korea, Japan, and Vietnam

 5. 229 Whitney           African fern pine (Afrocarpus falcatus, formerly A. gracilior), E & S Africa (peeking around the construction fence)

 6. 219 Whitney           Victorian box (Pittosporum undulatum), E Australia (common in the neighborhood; intensely fragrant white flowers cycle through the year)

 7. 191 Fairmount        Tree fuchsia (Fuchsia arborescens), C America (peeking over the fence on Whitney; this large shrubby fuchsia flowers all year in SF)

 8. 191 Fairmount        Peppermint willow (Agonis flexuosa), SW Australia (2 trees is on Whitney)

 Whitney Street, Fairmount to Randall, east side

Water gum (Tristaniopsis laurina)

9. 159 Whitney           Water gum (Tristaniopsis laurina), E Australia (this tree grows in stream-side locations in the wild, hence the common name; SF’s most commonly planted street tree)

 10. 155 Whitney          Mayten (Maytenus boaria), Chile

 11. 119 Whitney          Coast redwood (Sequoia sempervirens), Big Sur to SW Oregon; CA coastal native (this species is the tallest tree in the world)

 12. 197 Randall           Plume albizia (Paraserianthes lophantha, formerly Albizia lophantha), SW Australia (within the fenced garden of the property on Randall; a feathery-leafed small tree with pale yellow flowers in clusters; this species has become a weed in the western portions of Golden Gate Park and above Sutro Baths)

 **Cross Whitney and continue a short distance on Randall**

 Randall Street, Whitney to Sanchez, south side, then north side

13. 201 Randall           Ray Hartman ceanothus (Ceanothus ‘Ray Hartman’), hybrid of CA native species (just beginning to open its blue flowers)

 14. 207 Randall           Indian laurel fig (Ficus microcarpa ‘Nitida’), S Asia to N Australia (formerly one of SF’s most planted trees)

 **Cross Randall**

 15. 200 Randall           Brazilian pepper tree (Schinus terebinthifolia), Brazil, Argentina, Paraguay

 16. 228 Randall           Lemon bottlebrush (Callistemon citrinus), E Australia

 17. 228 Randall           Giant yucca (Yucca gigantea, formerly Y. elephantipes), Mexico & Central America

 18. 240 Randall           New Zealand Christmas tree, pōhutukawa in Māori (Metrosideros excelsa), New Zealand (this tree flowers most reliably in summer months, which would be Christmas time in NZ, south of the equator)

 Randall Street, Sanchez to Harper, north side

Olive (Olea europaea)

19. 250 Randall           Olive (Olea europaea), Mediterranean Basin

 20. 250 Randall           Meyer lemon (Citrus x meyeri), hybrid of mandarin and pomelo, both SE Asian species (in the rear yard, heavily laden with fruit)

Meyer lemon (Citrus x meyeri)

 21. 270 Randall           Sweet viburnum (Viburnum odoratissimum), S, SE, and E. Asia (very uncommon in SF; usually a shrub)

 ** Cross Harper**

 Harper Street, Randall to Laidley, west side

Bailey’s acacia (Acacia baileyana ‘Purpurea’)

22. 76 Harper              Bailey’s acacia (Acacia baileyana ‘Purpurea’), E Australia (this is usually among the earliest flowering trees in SF, always beginning in January with fluffy bright yellow flowers)

 ** Cross Laidley**

 Laidley Street, Harper to Fairmount, south side

Chinese windmill palm (Trachycarpus fortunei)

23. 128 Laidley           Chinese windmill palm (Trachycarpus fortunei), China (a fine specimen)

 24. 117 Laidley           Texas privet (Ligustrum japonicum ‘Texanum’), E. Asia (2 trees across the street; city champions; these are usually seen as large sheared hedges)

 25. 138 Laidley           Cork oak (Quercus suber), Spain & Portugal (3 trees; the bark of this tree provides the cork used in wine bottles)

Cork oak (Quercus suber) - closeup of bark

 26. 140 Laidley           Black locust (Robinia pseudoacacia), E USA (this deciduous tree will have fragrant white flowers in spring)

 ** continue on the lower side of Laidley**

 Laidley Street, Fairmount to Miguel, east side (lower side)

a beautiful Victorian home on Laidley Street

27. 237 Fairmount      Willow-leaf peppermint (Eucalyptus nicholii), SE Australia (2 trees, one on each side of Laidley)

 28. 233 Laidley           Primrose tree (Lagunaria patersonii), Norfolk and Lord Howe islands (soft pink flowers will appear later in the year)

 29. 224 Laidley           Rusty-leaf fig (Ficus rubiginosa), E Australia (across the street)

Glossy privet (Ligustrum lucidum)

 30. 279 Laidley           Glossy privet (Ligustrum lucidum), S China (2 trees)

 Miguel Street, Laidley to Whitney, northeast side

31. 201 Miguel            Tree aloe (Aloidendron barberae, formerly Aloe bainesii), S Africa to Mozambique (this specimen appears to be variegated, but the effect is due to sunscald)

Tree aloe (Aloidendron barberae, formerly Aloe bainesii)

 32. 219 Miguel            Bronze loquat (Rhaphiolepis deflexa, syn. Eriobotrya deflexa), S China and Vietnam

 Whitney Street, north from Miguel, west side

33. 268 Whitney          Jacaranda (Jacaranda mimosifolia), Argentina and Bolivia (watch for the big show of blue purple flowers in summer; these heat loving trees are becoming more common in SF, especially in warmer areas like the Mission District—thanks in partto climate change)

 34. 260 Whitney          Marina strawberry tree (Arbutus ‘Marina’), hybrid of Mediterranean species (many fine specimens of this tree can be seen throughout the neighborhood; first introduced in San Francisco)

 Today’s tree walk ends here, just a few yards north of its beginning at Whitney and Chenery.

Our regular commercial: This walking tour was organized by Mike Sullivan, author of The Trees of San Francisco and webmaster of www.sftrees.com; Jason Dewees, horticulturist at Flora Grubb Gardens and author of Designing with Palms; Richard Turner, retired editor of Pacific Horticulture magazine and Sairus Patel, soon to be author of Trees of Stanford and Environs. You can follow Mike and Jason on their tree-themed Instagram pages at @sftreeguy and @loulufan. Richard edited another great book on San Francisco trees: Elizabeth McClintock’s Trees of Golden Gate Park. If you’re a tree enthusiast, buy all four of these books!

Top photos of this blog's first decade!

I noticed recently that this blog just had a 10 year anniversary - my first post was August 30, 2013. I scrolled through the decade of posts, and found some photos that made me smile. Here are my top sftrees.com photos from the last 10 years:

Spotted gum (Corymbia maculata) adjacent to the Mission Pool at 19th Street between Guererro and Valencia. What a spectacular tree!

The largest Monterey cypress in the country! That’s me under the tree - In March 2021 I did a pilgrimage to see this amazing tree. It’s located at 751 Pescadero Creek Road in Pescadero - about 8 miles inland from Highway 1.

May 2020 - Jason Dewees (left), Richard Turner (right) and me on our Potrero Hill tour, next to a purple smoke tree (Cotinus coggygria ‘Royal Purple’). That’s a box of chalk in my hand. This was in the depths of the pandemic, so we were doing our chalk tree tours with masks.

The yellow-blooming New Zealand Christmas tree (Metrosideros excelsa) at 1221 Stanyan Street. My favorite individual tree in San Francisco.

A silk oak leaf on the sidewalk at 3520 18th/Valencia in the Mission

A red flowering gum (Corymbia ficifolia) on Monterey Boulevard in St. Francisco Woods. I love this species in San Francisco more than any other. Why is the City restricting the planting of this tree??!

Garage on Grove Street in the NOPA neighborhood

A stately wine palm (Jubaea chilensis) at the Sunnyside Conservatory on Monterey Boulevard. It takes a LONG time for this palm species to get this tall.

And another palm - this time a Mexican fan palm (Washingtonia robusta) in MissionBay

A doodle, courtesy of Jason Dewees

The California buckeye (Aesculus californica) at 2694 McAllister/Willard Street - largest and probably oldest of its species in San Francisco. Sadly, this tree died over the 2022/2023 winter. Here it is in glorious bloom in June 2020.

A dawn redwood (Metasequoia glyptostroboides) in the Arnold Arboretum in Boston in August 2021 - that’s my sister Patricia under the tree for scale. The Arnold Arboretum organized the effort to bring seeds back from China after the tree was discovered in the 1940s, and this tree was planted in 1948 when the seeds arrived. This is the largest one in the arboretum, and since their trees were planted first, it may be the largest dawn redwood in the United States!

sidewalk imprint of a London plane leaf on Page Street in the Haight-Ashbury neighborhood

California buckeye (Aesculus californica) on Poppy Lane in Glen Park

tulip tree (Liriodendron tulipifera) at the corner of Kearny and Vallejo on Telegraph Hill

gold medallion tree (Cassia leptophylla) at 227 Cole in the NOPA neighborhood. This one is the “City Champion” - biggest of the species in San Francisco

Beautiful garage door artwork at 523 Precita near Precita Park (the owner is the artist!)

  Monterey pine (Pinus radiata) at 214 Santa Clara Avenue. This specimen is the largest in the Western Hemisphere!

My husband and I took a trip to Sicily in April 2022 - this is a Moreton bay fig (Ficus macrophylla v. columnaris) in the Palermo botanical gardeny. That’s me standing behind one of the buttressing roots of the tree.

a carob tree (Ceratonia siliqua) in a field in Sicily

a silk floss tree (Ceiba speciosa) in Prospect Park in the Dogpatch neighborhood

a lonely volunteer California poppy in a San Francisco sidewalk

Row of Victorians off Page Street in the Haight Ashbury neighborhood

and just down the street on Page, Spiral aloe (Aloe polyphylla) at 1124 Page Street

the four of us! Jason Dewees, Sairus Patell, Mike Sullivan and Richard Turner

a lovely Guadalupe palm (Brahea edulis) at 333 Sussex Street in Glen Park

take a rock in Telegraph Hill!

Trees of Copenhagen

I visited Copenhagen in July 2023, and found some remarkable trees in the four days that I was there, all in the central part of the city. Some were in Copenhagen’s very nice botanical garden, some in the King’s Garden, one in the city’s best art museum (!), and one in a pot just outside the home where we stayed. See below!

Lavalle hawthorns (Crataegus X lavallei) adjacent to the Little Mermaid

Perhaps the most famous tourist attraction in Copenhagen is the “Little Mermaid”. Some of our friends told us not to bother, but we were strolling along the water on our first day in the City, and ran across it. Just adjacent to the Little Mermaid was a small grove of Lavalle hawthorns (Crataegus X lavallei).

The King’s Garden (also known as Rosenborg Garden) in central Copenhagen is the oldest and most visited park in central Copenhagen - it was established in the early 17th century as the private garden of King Christian IV's Rosenborg Castle, which is adjacent. It’s full of stately mature trees that are happy in northern Europe.

White willow (Salix alba) in the King’s Garden

Common lime or European lime (Tilia X Europaea) in the King’s Garden

I don’t normally expect to find landmark trees in art museums, but just inside the entrance to the Glyptoteket (Copenhagen’s best art museum) was this nice example specimen of a Canary Island date palm (Phoenix canariensis).

Canary Island date palm (Phoenix canariensis) in the Glyptoteket

And Copenhagen has a lovely botanical garden in center city. It was raining off and on the day I visited, but in between the showers I found some trees worth noting. Just inside the gate on the left was an empress tree (Pawlonia tomentosa) - easily identifiable by the huge leaves and distinctive seeds.

empress tree (Pawlonia tomentosa)

empress tree - closeup of leaves and fruits

If you stay to the left after entering the garden, eventually you will reach this sweet chestnut tree (Castanea sativa). I didn’t find man of these in Scandinavia on our trip, so it caught my eye.

sweet chestnut (Castanea sativa)

sweet chestnut (closeup - leaves and fruits)

I think the most impressive grouping of trees were on a small hill near the center of the garden. Side by side were two trees that are actually fairly close relatives - a dawn redwood (Metasequoia glyptostroboides) right next to a coast redwood (Sequoia sempervirens). The coast redwood is the tallest tree in the world, and the dawn redwood was thought to have been extinct (known only from fossil records) until a specimen was discovered in central China in 1941.

A dawn redwood (Metasequoia glyptostroboides) on the left, right next to a coast redwood (Sequoia sempervirens) on the right

And just behind these two, another close relative of both - a giant sequoia (Sequoiadendron giganteum), native to the Sierra Nevada Mountains of Central California. This is the tree that is the most massive tree in the world, and it was in the bloom of health here in Copenhagen!

giant sequoia (Sequoiadendron giganteum)

We stayed very close to “Churchillparken” (Churchill Park) in Copenhagen, and as I meandered there one day, I ran across this spectacular specimen of sycamore maple (Acer pseudoplatanus). We don’t see this tree much in my hometown of San Francisco, so it was a treat to find it (and many others nearby).

sycamore maple (Acer pseudoplatanus) in Churchillparken (Churchill park)

And not too far away, next to one of the many canals, a weeping willow (Salix babylonica).

weeping willow (Salix babylonica) in Churchill Park

And finally, I think it’s a little cold for this tree in Copenhagen, but just outside the home where we were staying was this baby monkey puzzle tree (Araucaria araucana). I’m sure it will be brought inside for the winter!

monkey puzzle tree (Araucaria araucana)

Valencia - Guerrero Tree Tour

 

Yes, another chilly, overcast, and ridiculously windy summer day in San Francisco… We chose to focus today’s walk on a portion of the Mission District that merges with the Liberty Hill Historic District, between 19th and 23rd streets and between Valencia and Guerrero streets. We have touched on this neighborhood before, but this tour focused on the blocks between Valencia and Guerrero. In addition to some striking mature trees and magnificent Victorian-era homes in the Liberty Hill area, there are plenty of appealing dining and drinking establishments to enjoy along Valencia Street.

 Today’s walk begins in front of the Mission Pool and Playground, on 19th Street at Linda Street. Head east on 19th to Valencia Street, then south on Valencia to 20th Street. Head west on 20th to Guerrero, then south on Guerrero to Liberty Street, and east on Liberty back to Valencia. Continue south on Valencia to 21st Street, west on 21st to Guerrero, south again on Guerrero to Hill Street, east on Hill to Valencia, south on Valencia to 22nd, and east on 22nd to Guerrero again. At Guerrero, cross 22nd and head back east on 22nd to San Jose Avenue, then south on San Jose to Alvarado Street, west briefly on Alvarado and then back to San Jose. Head south on San Jose to the SW corner of 23rd Street. The tour ends here; unlike most of our tours, this is a one-way route, not a loop. Go back to Valencia to return to the start of the tour. This one-way walk is under two miles in length.

 Numbered trees are labeled with common and scientific names and country of origin, all written in white chalk on the sidewalk; accompanying numbers, in blue, run from 1 to 45. White arrows on the pavement provide directions whenever a turn is needed.

 19th Street, Linda to Valencia, north side

Spotted gum (Corymbia maculata)

1. 19th at Linda          We decided to start our tour with one of our favorite trees in San Francisco. This spotted gum (Corymbia maculata) is the tall tree with almost white bark, against the building). It’s native to eastern Australia - and this tree made it onto my “top 10” list of all of San Francisco’s trees!   

 2. 3543 - 19th              English walnut (Juglans regia), Balkans, Iran, and India to Central China (tree is in the rear yard of the blue house; the best walnut for eating)

 3. 3519 - 19th              Weeping bottlebrush (Callistemon viminalis), E Australia (an uncommonly tall specimen)      

 4. 3519 - 19th              Chinese pistache (Pistacia chinensis), W & C China (not commonly planted in SF, since it prefers greater summer heat to develop its spectacular fall foliage colors)

Chinaberry (Melia azederach)

 5. 3505 - 19th              Chinaberry (Melia azedarach), S Asia to Australia (2 trees, the only ones in SF; a weed elsewhere; one of the few trees in the mahogany family found in SF)

 Valencia Street, 19th to 20th, west side

6. 850 Valencia           Shiny xylosma (Xylosma congestum), China (3 trees along the northern fence line within the park; rare in SF; often grown as a large shrub)

Shiny xylosma (Xylosma congestum)

 7. 850 Valencia           Freeman maple (Acer x freemanii), hybrid of Acer rubrum & Acer saccharinum, both from E North America (3 trees in the sidewalk in front of the Mission Playground)

 20th Street, Valencia to Guerrero, south side

Norfolk Island pine (Araucaria heterophylla)

8. 3635 - 20th               Norfolk Island pine (Araucaria heterophylla), Norfolk Island, South Pacific

 9. 3653 - 20th              Primrose tree (Lagunaria patersonia), Norfolk and Lord Howe islands (soft pink flowers will begin appearing soon)

 Guerrero Street, 20th to Liberty, east side

Mulberry (Morus alba)

10. 823 Guerrero         Mulberry (Morus alba), China (tree is across the street; the large leaves are the only food of the silkworm, from whose cocoons we get silk thread)

 11. 827 Guerrero         Cabbage tree (Sonchus brassicifolius), Juan Fernandez Islands, Chile (short tree with large roundish lives, just above the wall; extremely rare in SF)

Blue Atlas cedar (Cedrus atlantica ‘Glauca’)

 12. 827 Guerrero         Blue Atlas cedar (Cedrus atlantica ‘Glauca’), Atlas Mountains of Morocco & Algeria

 Liberty Street, Guerrero to Valencia, north side

13. 845 Guerrero         Ginkgo (Ginkgo biloba), China (these 3 trees are all females; note the fruits developing; when ripe, they will be exceedingly foul-smelling)

 14. 82 Liberty              New Zealand Christmas tree, pōhutukawa in Māori (Metrosideros excelsa), New Zealand (this tree flowers most reliably in summer months, which would be Christmas time in NZ, south of the equator)

New Zealand Christmas tree, pōhutukawa in Māori (Metrosideros excelsa)

 15. 82 Liberty              Indian laurel fig (Ficus microcarpa ‘Nitida’), S Asia to N Australia (formerly one of SF’s most planted trees)

 16. 50 Liberty              Shamel ash (Fraxinus uhdei), Mexico to Central America (much of the street is planted with these trees, many of which were pollarded at some point in their lives)

 **Continue south on Valencia to 21st

 21st Street, Valencia to Guerrero, south side

17. 3325 - 21st             Lemon bottlebrush (Callistemon citrinus), E Australia (a row of several trees)

 ** Note the row of beautiful ginkgos in the middle of this block

 Guerrero Street, 21st to Hill, east side

Douglas fir (Pseudotsuga menziesii)

18. 906 Guerrero         Douglas fir (Pseudotsuga menziesii), West Coast & Rocky Mountains to S Mexico (tall conifer with needle-like leaves across the street; a CA native tree!)

 19. 940 Guerrero         Camphor trees (Cinnamomum camphora), E and SE Asia (two trees across the street, recently pruned to be quite open; this tree prefers more summer warmth and is seldom planted in SF)

 20. Guerrero median  Shoestring acacia (Acacia stenophylla), Australia, mostly in the interior of the continent (many trees are planted in the median for several blocks of Guerrero; long slender leaves)

 Hill Street, Guerrero to Valencia, south side

21. 99 Hill                   Jacaranda (Jacaranda mimosifolia), Argentina, Bolivia, Brazil (watch for the big show of blue purple flowers soon; these heat loving trees are becoming more common in SF, especially in warmer areas like the Mission District—all thanks to climate change)

 22. 949 Guerrero         Raywood ash (Fraxinus augustifolia ‘Raywood’), C & S Europe, NW Africa, SW Asia (tree is on the north side of Hill Street; a selected seedling found in a South Australia garden)

 23. 87 Hill                   Japanese camellia (Camellia japonica), E Asia (though usually grown as a shrub for its beautiful late winter/spring flowers, Japanese camellia is actually a small tree; note shrubby forms in front of the neighboring house)

Beautiful Mexican marigold (Tagetes lemmonii) on the north side of Hill Street

 24. 83 Hill                   Purple-leaf plum (Prunus cerasifera), Eurasia (pink flowers usually appear by February; formerly SF’s most planted street tree; totally without leaves through fall and winter)

 25. 53 Hill                   London plane tree (Platanus x hispanica, formerly Platanus x acerifolia), hybrid of E USA species and European species; it is among the most commonly planted trees in cities around the world)

 26. 49 Hill                   Japanese maple (Acer palmatum), Korea and Japan

Marina strawberry tree (Arbutus ‘Marina’)

 27. 41 Hill                   Marina strawberry tree (Arbutus ‘Marina’), hybrid of Mediterranean species (this hybrid was first introduced in San Francisco)

Closeup of flowers of Marina strawberry tree (Arbutus ‘Marina’)

 28. 25 Hill                   Australian willow or wilga (Geijera parviflora), E & SE Australia (this tree generally prefers the warmth of the eastern parts of the city). This is the best example of this species in San Francisco that we’ve found!

 29. 1 Hill                     Mexican fan palm (Washingtonia robusta), Baja California & Sonora, Mexico (2 trees trees with short trunks; California’s most commonly planted palm)

Mexican fan palm (Washingtonia robusta)

 Valencia Street, Hill to 22nd, west side

30. 1098 Valencia        Brisbane box (Lophostemon confertus), E Australia

 22nd Street, Valencia to Guerrero, north side

31. 1098 Valencia        Hybrid Fogg michelia (Magnolia x foggii), hybrid of Asian species, M. figo and M. doltsopa (tree is on 22nd; watch for fragrant white flowers opening from the furry brown buds)

 32. 3326 - 22nd            Paradox walnut (Juglans hindsii x J. regia), hybrid of CA native and European species (2 trees; be sure to read the story about them in the shop window)

Paradox walnut (Juglans hindsii x J, regia)

 33. 3334 - 22nd            Prickly melaleuca (Melaleuca styphelioides), E Australia                    (note the tiny prickly leaves, white flowers, and spongy park)

Ginkgo (Ginkgo biloba),

 34. 3342 - 22nd            Ginkgo (Ginkgo biloba), China (one of SF’s best specimens)

 35. 3368 - 22nd            Jewel yucca (Yucca gigantea ‘Jewel’), Central America (in the bright yellow containers; note the striped, or variegated, leaves)

The Lone Palm of the Lone Palm!! Mule palm (Butia odorata x Syagrus romanzoffiana)

 36. 3394 - 22nd            Mule palm (Butia odorata x Syagrus romanzoffiana), a hybrid of Brazilian species (very uncommon)

I love the doorway of the Lone Palm bar :)

 22nd Street, Guerrero to San Jose, south side

Giant yucca (Yucca gigantea, formerly Y. elephantipes)

37. 1001 Guerrero       Giant yucca (Yucca gigantea, formerly Y. elephantipes), Mexico & Central America (tree is on 22nd Street; all-green leaves)

 38. 3365 - 22nd            Victorian box (Pittosporum undulatum), E Australia (intensely fragrant white flowers cycle through the year)

Victorian box (Pittosporum undulatum)

 39. 3345 - 22nd            Red maple (Acer rubrum), Eastern North America

 **Head south on San Jose Avenue, turning right on Alvarado Street

 Alvarado Street, east of San Jose, north side

40. 36 Alvarado          Natchez crape myrtle (Lagerstroemia x ‘Natchez’), hybrid of E Asian species (developed by the National Arboretum in DC; notable for its beautifully mottled bark, outstanding fall color, and its mildew-resistant foliage, making it a good choice for SF; its flowers are white, in late summer)

 *** Cross Alvarado carefully***

 Alvarado Street, east of San Jose, south side

41. 37 Alvarado          Queen palm (Syagrus romanzoffiana), S Brazil

 42. 50 San Jose            Southern magnolia (Magnolia grandiflora), SE USA (2 trees on Alvarado Street)

 **Continue south on San Jose to 23rd Street

 San Jose Avenue at 23rd, west side

43. 3503 - 23rd            Silver Atlas palm (Chamaerops humilis var. argentea), Atlas Mountains of Morocco & Algeria (trees are above the wall on San Jose; low, shrubby palms with silvery cast to the foliage)

 44. 3503 - 23rd            Waggie palm (Trachycarpus fortunei ‘Wagnerianus’), cultivar of a Chinese species (taller palms above the wall on San Jose)

                                     Knife-leaf wattle (Acacia cultriformis), E Australia (row of small trees above the wall on San Jose; watch for yellow flowers in winter)

Pasopaya palms (Parajubaea torallyi)

 45. 3503 - 23rd            Pasopaya palms (Parajubaea torallyi), Bolivian Andes (5 trees in a row along San Jose; very rare)

 This tree walk ends here. To return to its beginning, head back to Valencia and turn left; follow Valencia back to 19th and turn left toward the Mission Pool.

Our regular commercial: This walking tour was organized by Mike Sullivan, author of The Trees of San Francisco and webmaster of www.sftrees.com; Jason Dewees, horticulturist at Flora Grubb Gardens and author of Designing with Palms; Richard Turner, retired editor of Pacific Horticulture magazine and Sairus Patel, soon to be author of Trees of Stanford and Environs. You can follow Mike and Jason on their tree-themed Instagram pages at @sftreeguy and @loulufan. Richard edited another great book on San Francisco trees: Elizabeth McClintock’s Trees of Golden Gate Park. If you’re a tree enthusiast, buy all four of these books!

New Zealand Christmas trees at peak bloom

17th Street near Ord, north side

New Zealand Christmas trees (Metrosideros excelsa), known as pōhutukawa in their native New Zealand, love San Francisco’s cool maritime climate - and they’re in full bloom right now (early July - a little bit late this year!). New Zealand Christmas trees are in the myrtle family, and are relatives of the eucalyptus and other trees with “bottlebrush”-type flowers (what you’re seeing in the flowers are not petals, but the male stamens of the tree). Almost all of the thousands of New Zealand Christmas on the streets of San Francisco have red blooms, but there’s one tree at 1221 Stanyan Street in Cole Valley that puts on a show with eye-popping yellow flowers.

1221 Stanyan Street

How did this tree end up with yellow flowers? The story goes back to Victor Reiter, San Francisco’s most famous plantsman from the 1940s until his death in 1986. In 1940, there was a natural mutation of the species on tiny Motiti Island in the Bay of Plenty in New Zealand. Reiter was one of the first Californians to obtain a cutting - from a friend who happened to be visiting New Zealand. As the Reiter family lived in several homes in a three-block stretch of Stanyan Street, they planted the curiosity in front of their 1221 Stanyan address—still occupied today by a family member. And more than 70 years later, the tree is thriving. It’s a beautiful mutant with an amazing history and pedigree—and my favorite tree in San Francisco.

flowers with the characteristic aerial roots of this tree

Castro/Noe Summit Tree Tour (6-4-23)

 

Finally, a bright sunny day in San Francisco! And a beautiful hilltop from which to enjoy the weather and the views. We chose the hill that separates Noe Valley from Eureka Valley and the Castro. To put it another way, we are at the divide between Islais Creek and Mission Creek watersheds. This neighborhood of beautiful homes and small but richly planted front gardens also offers an array of interesting trees around which to develop today’s walk. (Don’t miss the views.) 

Today’s walk begins at the northwestern corner of Castro and 22nd streets. Head west (uphill) on 22nd to the base of the steps, then cross the street and return to Castro. Head north on Castro to Hill Street, then cross Castro and head east on Hill to Noe Street. At Noe, turn left and continue north to 21st Street. Head east on 21st to Sanchez Street, then south on Sanchez to Hill, west on Hill to Noe, south on Noe to 22nd, and west on 22nd to the start of the tour at Castro. This walk is just over a mile in length.

 Numbered trees are labeled with common and scientific names and country of origin, all written in white chalk on the sidewalk; accompanying numbers, in blue, run from 1 to 52. White arrows on the pavement provide directions whenever a turn is needed. 

This walking tour was organized by Mike Sullivan, author of The Trees of San Francisco and webmaster of www.sftrees.com; Jason Dewees, horticulturist at Flora Grubb Gardens and author of Designing with Palms; Richard Turner, retired editor of Pacific Horticulture magazine and Sairus Patel, soon-to-be editor of Trees of Stanford and Environs.  You can follow Mike and Jason on their tree-themed Instagram pages at @sftreeguy and @loulufan. One other great book on San Francisco trees, while you’re at it: Elizabeth McClintock’s Trees of Golden Gate Park, edited by Richard Turner. If you’re a tree enthusiast, buy all three books!”

A beautiful garden on 22nd Street just uphill from Castro Street

22nd Street, west of Castro, north side

1. 3900 - 22nd             Edible fig tree (Ficus carica), Mediterranean Basin & Middle East (note the first crop of fruit already developing on the upper branches)     

 2. 3900 - 22nd             Monterey cypress (Hesperocyparis macrocarpa), Carmel, CA (one of the three most commonly planted trees in SF’s parks)

 3. 3900 - 22nd             Italian cypress (Cupressus sempervivens ‘Glauca’), E Mediterranean (2 candle-shaped conifers next to the sidewalk)

Tree of heaven (Ailanthus altissima)

 4. 3900 - 22nd              Tree of heaven (Ailanthus altissima), China (one of the weediest trees in the country, often covering vast areas of disturbed land, such as in the gold mining districts of the Sierran foothills). Very rare in San Francisco - this is only the 2nd example of the tree that I know of!

Cook pine (Araucaria columnaris)

 5. 3910 - 22nd             Cook pine (Araucaria columnaris), New Caledonia (similar to Norfolk Island pine, but this narrower, denser species always has a curve at the base of the trunk and a pronounced lean toward the equator). In the southern hemisphere, it leans north, but this tree is dutifully leaning in a southward direction.

 6. 3932 - 22nd             Canary Island date palm (Phoenix canariensis), Canary Islands, Spain (this is the species seen on Market Street and along the Embarcadero)

Canary Island date palm (Phoenix canariensis)

 7. 3938 - 22nd             Yew-plum pine, Buddhist pine, or Japanese podocarpus (Podocarpus macrophyllus), Japan & China

 **Cross to the south side of 22nd Street, after gazing on the 22nd Street Jungle Steps (planted with mostly California native plants)

 22nd Street, west of Castro, south side

8. 3917 - 22nd             Fern pine (Afrocarpus gracilior), E & S Africa (one of the tidiest of trees, with seldom any litter from leaves, flowers, or fruits)

 9. 3911 - 22nd             Elegant water gum (Tristaniopsis laurina ‘Elegant’), E Australia (this selection of the water gum has longer, glossier leaves than the species)

 Castro Street, 22nd to Hill, west side

10. 3900 - 22nd            Coast silk tassel (Garrya elliptica), coastal CA native, from Big Sur to central             Oregon (watch for the flowers in winter, long pendant creamy white tassels; normally a large shrub, this one is being shaped into a small tree)

 11. 850 Castro             Corkscrew willow (Salix matsudana ‘Tortuosa’), China and Korea (notable for the irregular curves and twists in the stems; popular with flower arrangers)

 **Cross Castro at the crosswalk

 Hill Street, Castro to Noe, north side

London plane tree (Platanus x hispanica)

12. 847 Castro             London plane tree (Platanus x hispanica), hybrid of E USA species and European species; it is among the most commonly planted trees in cities around the world)

 13. 584 Hill                 Jacaranda (Jacaranda mimosifolia), Argentina, Bolivia, Brazil (leafless now, but watch for the big show of blue purple flowers soon; these heat loving trees were seldom seen in Noe Valley until about 20 years ago; now there are quite a few, and they seem happy—all thanks to climate change)

 14. 576 Hill                 Red-flowering gum (Corymbia ficifolia), SW Australia (produces bright red, orange, or pink flowers in summer; among the showiest of trees in SF’s urban forest, we cannot understand why the city is no longer planting this amazing tree)

Peppermint willow (Agonis flexuosa)

 15. 574 Hill                 Peppermint willow (Agonis flexuosa), SW Australia (break a leaf to smell the peppermint, and enjoy the small white flowers)

 16. 544 Hill                 Ginkgo (Ginkgo biloba), China (last of an ancient lineage of gymnosperms)

 17. 534-536 Hill           Southern magnolia (Magnolia grandiflora), SE USA (2 trees)

 18. 512 Hill                 Pygmy date palm (Phoenix roebelenii), S China, Laos, Vietnam

 19. 510 Hill                 Chinese elm (Ulmus parvifolia), China, Korea, Japan, and Vietnam

Chinese elm (Ulmus parvifolia)

 Noe Street, Hill to 21st, west side

20. 818 Noe                 Boxleaf azara (Azara microphylla), Chile (this delicate looking small tree has tiny white fragrant flowers in winter)

 21. 818 Noe                 New Zealand Christmas tree, pōhutukawa in Māori (Metrosideros excelsa), New Zealand (this tree flowers most reliably in summer months, which would be Christmas time in NZ, south of the equator)

 22. 3801 - 21st             Japanese crabapple (Malus floribunda), Japan (flowers heavily in early April)

 21st Street, Noe to Sanchez, south side

23. 3785 - 21st             Olive (Olea europaea), Mediterranean Basin

 24. 3785 - 21st             Waggie palm (Trachycarpus fortunei ‘Wagnerianus’), cultivar of a Chinese species

 25. 3781 - 21st             Purple Bailey’s acacia (Acacia baileyana ‘Purpurea’), E Australia (this is usually among the earliest flowering trees in SF, always beginning in January with fluffy yellow flowers)

Purple-leaf plum (Prunus cerasifera)

 26. 3775 - 21st             Purple-leaf plum (Prunus cerasifera), Eurasia (pink flowers usually appear by February; formerly SF’s most planted street tree; totally without leaves through fall and winter)

 27. 3767 - 21st             Italian stone pine (Pinus pinea), Mediterranean Basin (the source of pine nuts/pignoli)

 28. 3733 - 21st             Red-flowering gum hybrid (Corymbia ficifolia x calophylla), SW Australia

 29. 3721 - 21st             Cork oak (Quercus suber), Spain & Portugal (the bark of this tree provides the cork used in wine bottles)

 21st at Sanchez streets

Monterey cypress (Hesperocyparis macrocarpa)

29b. NW corner          Monterey cypress (Hesperocyparis macrocarpa), Carmel, CA (across the street; one of the three most commonly planted trees in SF’s parks)

Monterey pines (Pinus radiata) framing former Mayor Sonny Rolf’s home

 30. NE corner             Monterey pine (Pinus radiata), CA native: Año Nuevo, Monterey, Cambria, plus  Cedros and Guadalupe islands, MX (2 trees to the left of former Mayor Sonny Rolf’s home, diagonally across the intersection; most widely planted coniferous tree in the world, mostly for lumber.

 Sanchez Street, 21st to Hill, west side

31. 3701 - 21st             Dark Shadows tea tree (Leptospermum ‘Dark Shadows’), SE Australia

 32. 824 Sanchez          Shoestring acacia (Acacia stenophylla), Australia

 **Cross Sanchez to east side

 33. 849 Sanchez          After Dark peppermint willow (Agonis flexuosa ‘Jervis Bay Afterdark’), SW Australian cultivar (2 trees in front of the house; often less vigorous than the green-leafed species; compare with a mature specimen of the species at #15 on this walk)

 34. 849 Sanchez          Variegated Arabian candelabra tree (Euphorbia ammak ‘Variegata’), Yemen (2 trees in front of the house; sometimes called ghost cactus; however, this is not a cactus, but definitely a succulent)

 35. 849 Sanchez          Mediterranean fan palm (Chamaerops humilis), Mediterranean Basin: Portugal & Morocco to Tunisia & Italy (northernmost natural range of any palm in the world)

 36. 849 Sanchez          Beaked yucca (Yucca rostrata), Mexico and Texas (3 trees along Hill St; note the asparagus-like flower stalk rising from the center of two trees)

 Hill Street, Sanchez to Noe, north side

Chinese windmill palm (Trachycarpus fortunei)

37. 423 Hill                 Chinese windmill palm (Trachycarpus fortunei), China (across the street; note the “skirt” of dead leaves that have been left on the tree; the skirt helps protect the trunk of the tree)

 38. 426 Hill                 Brazilian pepper tree (Schinus terebinthifolia), Brazil, Argentina, Paraguay

 ** Cross Hill Street to south side

 39. 435 Hill                 Evergreen pear (Pyrus kawakamii), Taiwan (only in cold winters does this species lose its leaves in San Francisco)

 40. 437 Hill                  Red escallonia (Escallonia rubra), S Chile and Argentina, all the way to Tierra del Fuego (normally grown as a dense large shrub, this one has been pruned into an attractive multi-trunk tree)

 41. 467 Hill                 Silver dollar gum (Eucalyptus polyanthemos), E Australia

 Noe Street, Hill to 22nd, west side

[42 not used]

 43. 885 Noe                 Chinese pistache (Pistacia chinensis), W & C China (not commonly planted in SF since it prefers greater summer heat to develop its spectacular fall foliage colors)

American sweetgum (Liquidambar styraciflua)

 44. 870 Noe                American sweetgum (Liquidambar styraciflua), E USA to Mexico & Central America (across the street)

 45. 893 Noe                 Indian laurel fig (Ficus microcarpa ‘Nitida’), S Asia to N Australia (formerly one of SF’s most planted trees)

 46. 899 Noe                 Carob (Ceratonia siliqua), E Mediterranean Basin (tree is on 22nd St; seed pods can be used to make a chocolate substitute—though not recommended for true chocolate lovers)

 22nd Street, Noe to Castro, north side

47. 3806 - 22nd            Blackwood acacia (Acacia melanoxylon), SE Australia

 48. 3806 - 22nd            Little Gem magnolia (Magnolia grandiflora ‘Little Gem’), SE USA

 **Cross 22nd Street to the south side

 49. 3817 - 22nd            Saucer magnolia (Magnolia x soulangeana), hybrid of E Asian species, developed in France (large fragrant white flowers in spring)

 50. 3829 - 22nd            Japanese maple (Acer palmatum), Korea and Japan

 51. 3829 - 22nd            Victorian box (Pittosporum undulatum), E Australia (intensely fragrant white flowers cycle through the year)

Lemon bottlebrush (Callistemon citrinus)

 52. 3847 - 22nd            Lemon bottlebrush (Callistemon citrinus), E Australia

 This tree walk ends here, a few yards from its beginning at Castro and 22nd streets.

 

Guest Post: What Trees Should We Plant in San Francisco?

[NOTE: I recently read a letter to the editor of the SF Standard by my friend Jason Dewees (horticulturalist at Flora Grubb, and author of Designing With Palms). Jason was commenting on a story in the Standard about the effect of the the winter storms on San Francisco’s tree canopy, but his letter ranged wider than that, as you will see below. I thought the letter was so brilliant that it merited a wider audience - so with Jason’s permission, here it is - text below is all Jason’s.]

 The future of a thriving urban tree canopy in San Francisco lies not only in proper funding and care of trees along our streets, in our parks, and in public and private landscapes, but also in experimentation with and observation of exotic species for their adaptation to our increasingly variable, warming climate. 

The native flora of San Francisco features only two tree species with significant populations: coast live oak (Quercus agrifolia) and California buckeye (Aesculus californica). Other trees were and are indigenous within the current city limits of SF, like California bay laurel (Umbellularia californica) and madrone (Arbutus menziesii), but they were few and far between. Willows that grow in moist hollows and along stream courses can also achieve the size of trees. Beyond those woodlands, the land where the city was built was largely coastal scrub, prairie, marsh, and dunescape. Any tree native to California, but not to San Francisco, would essentially be an exotic tree for the city. That would include the many Monterey pines, Monterey cypress, coast redwoods, and other California trees creating a sylvan setting in our parks and open spaces.

One of the best places to experience the extant native coast live oak woodland of San Francisco is in the northeast swath of Golden Gate Park, especially in the hollow just to the west of the Arguello Gate. Buena Vista Park also harbors fragments of native oak woodland. In the Presidio, extensive oak woodland can be seen near Lobos Creek. These are enchanting, even magical, places, with complex layers of plants, animals, birds, lichens, fungi, and countless unseen organisms. Coast live oaks live in gardens inside many city blocks, planted by scrub jays and squirrels from native mother trees. The reputation of SF's pre-European landscape as barren and treeless is overblown.

The streets of San Francisco today would be much more bare of trees were it not for the importation of exotic species from around the world. From Australia, New Zealand, South Africa, China, the Himalayas, the Mediterranean Basin, Chile, Brazil, Mexico, North America, elsewhere in California, and beyond, horticulturists and scientists have introduced trees that tolerate or thrive in our peculiar climate. 

The combination of annual summer drought, cool, windy summers, mild, nearly frost-free winters, and now-erratic rainy seasons makes for unusual conditions. Our climate does not conform to expectations set by Anglo-American cultural heritage, in which summer rainfall and winter cold are viewed as the norm. Thanks to our famous fog, San Francisco enjoys year-round high humidity (comparable to Miami's, in fact), along with other coastal communities in Central and Northern California, but our position at the Golden Gate exposes us to more consistent summer winds than many other coastal California spots. Our climate is most comparable to that of Valparaíso, Chile, in its mildness and rainfall pattern. 

Some plants commonly grown at our latitude, even just inland where summers are warm, do not thrive in the mild temperatures here. And many trees that thrive here fail in the frostier winters and hot, dry summers of Livermore or Sacramento. The New Zealand Christmas tree or pōhutukawa (Metrosideros excelsa) is one of the most common and successful street trees in San Francisco, but its origins on the coastal bluffs of New Zealand did not prepare it to endure the freezing temperatures and hot, dry summers inland, where it perishes within a few years of planting. Callery pears (Pyrus calleryana)—originally from China and Vietnam—planted in San Francisco fail to burst into bloom, leaf out, produce fall color, or drop their leaves on the seasonal cycle seen on their fellow-clones planted as close as San Mateo or Corte Madera. Even coast redwoods (Sequoia sempervirens), not native to San Francisco proper, suffer without irrigation in some parts of the city, and have had to be removed; wind tends to stunt their top growth in exposed areas, even when otherwise thriving.

Residents may find it surprising that species like giant sequoia (Sequoiadendron giganteum) are growing here by the score in parks and backyards, surviving in a snowless, coastal environment, or that tropical ficus species (Ficus microcarpa) that become banyans in Hawai`i are a very common (and now problematic) street tree. Similarly, it comes as a surprise to many to learn that so many palms do well in San Francisco. Among the 2500 species in the palm family are species that range from 43 degrees north latitude (the Mediterranean fan palm, Chamaerops humilis), to 44 degrees south (the nīkau, Rhopalostylis sapida), and from sea level to 11,400 elevation in the equatorial Andes, where the climate is constantly chilly and misty. The designation of the palm as singularly exotic is based on its conspicuous form; almost all the urban tree species of San Francisco are exotic—that is, not native here. Some, like those ficus, are members of plant families that do not occur in the state or our biogeographic region. This is not the case with palms, of which one species is native to the state (the California fan palm, Washingtonia filifera) and another to the California floristic province (the Guadalupe palm, Brahea edulis). To continue to experiment with “native but exotic” species (such as some of the Southern California oaks) would help us figure out what species might really thrive in this ever-changing climate. Planting an urban forest is not a one-stop deal; the forest will always require monitoring and adapting for changing times.

The future of a thriving urban tree canopy in San Francisco lies not only in proper funding and care of trees along our streets, in our parks, and in public and private landscapes, but also in experimentation with and observation of exotic species for their adaptation to our increasingly variable, warming climate and our varied soils, and tolerance of and suitability for urban life. Among the most promising new street-tree introductions include oaks exotic to San Francisco. One, native to the Channel Islands and Guadalupe Island off Southern California and Baja, is the Island oak, Quercus tomentella, a fast-growing tree with an upright form in youth, tolerance of wind, drought, and fog, and luxuriant evergreen leaves. Other oaks from Mexico, Arizona, and even Texas have been planted in local botanical gardens and parks and as street trees in other California communities and may soon begin appearing in San Francisco.

Jason Dewees