Pacific Heights. The Castro. Potrero Hill. The city's 30-plus neighborhoods are famous for their variety of styles and moods. One has rainbow flags, another gaudy mansions, a third great sushi restaurants, a fourth strip clubs, a fifth art museums, and so on. The neighborhoods are distinct in terms of topography and microclimate, too, and to the discerning eye, they're distinct because of their trees.

Here's a quick rundown in Sullivan's own words:

Cole Valley (Sullivan's home neighborhood): "It's one of the densest parts of our urban forest and has some of the best trees and diversity -- people here absolutely love trees!"

Mission District: "A warm part of the city with good soils and less wind and fog. You see some types of eucalyptus that love warmth. Also, the jacaranda tree from Brazil with its great purple flowers."

Outer Richmond: "Really tough for trees. If there are, say, 100 species that will do well in San Francisco, there are maybe 10 that will do well in the Outer Richmond. They tend to do better on the north-south streets because those streets are protected from the winds coming off the ocean. The east-west streets out there are just death for trees."

North Beach: "It's a dense neighborhood so there isn't a lot of room for big trees. You don't see as much of the little craftsman cottage with a single-family owner who lovingly plants an unusual tree. There's a little less diversity here, more of the so-called 'normal trees' like the ficus and Brisbane box."

Financial District: "Surprisingly, it's got some amazing trees. The city's largest gingko is down here, the largest bay tree too. And there're gorgeous tulip trees around the old Federal Reserve at Sacramento and Battery."

For the gourmand, this city has olive and avocado and lemon trees, as well as Italian stone pines, a species whose seeds humans have been harvesting for an estimated 500,000 years. For the crafty, there are cork oaks, from which wine corks are made, and black walnuts, a native of the Eastern United States used in furniture and rifle stocks. And for the flowery, there are hawthorns, gums, magnolias, plums, acacias and bottlebrushes -- thousands upon thousands of blossoms coloring the streets all through the year.

The deodar cedar at 625 St. Francis Boulevard is a native of the Himalayas and takes its name from the Sanskrit devadara, meaning "tree of the gods." The New Zealand Christmas tree at 1221 Stanyan (Sullivan's favorite tree in the entire city) is an extremely rare "Aurea" variety that blooms yellow rather than the normal red. Catalina ironwoods grow beside a church on Connecticut Street. Strawberry trees front the German Consulate General on Jackson Street.

And at 17th and Folsom, nearing the end of the walking tour though the crowded, noisy, mural-splashed Mission District, there's an otherwise dismal parking lot fringed with floss silk trees, flame trees, bottle trees and mountain she-oaks. A block away, you can buy coffee and a pastry, sustenance while you linger in this surprising oasis. The trees rise up through holes in the filthy sidewalk, their branches brushing at power lines and pigeons, and above it all they reach for the sky. Look around.

The flame tree's lobed leaves are larger than your hand. The mountain she-oak is as magical as she sounds, her crown of droopy needles almost the color of rust. A homeless man sleeps in a cardboard bed. A red-shouldered hawk flies by, pursued by seagulls. The floss silk tree here at the corner -- this crazy one with the thorns erupting from smooth bark -- has been vandalized, graffitied up and down. No worries. When it flowers in a couple of months, the taggers' black scrawls will contrast nicely with the magenta blossoms.

Leath Tonino’s writing has appeared or is forthcoming in Orion, Sierra, The Sun and other magazines. He recently finished a series of essays about a year traveling the length of his home state Vermont by hiking, hitchhiking, skiing, biking, canoeing, swimming and flying. For the time being, he lives in San Francisco, Calif.