Lichens of Madison Heights

The lichens of where? Madison Heights is in southern Pasadena, a pretty residential neighborhood of quiet streets lined with shady camphor trees. Unfortunately this beautiful little area is smack in the middle of some of the worst air pollution in North America Los Angeles. So one with a critical eye for this sort of thing will notice before long that there's something missing.

Lichens.

For several years I have searched high and low (literally) for sign of them. They can't all be gone, right? And my patience has been rewarded with no fewer than four species to date (possibly five, but more on that later). But you have to know exactly where to look, and even then there are specimens that I will only find about 70% of the time I go to check up on them! One of them I found only after taking a photograph of another; imagine my surprise to find a few tiny black specks in the corner of my frame when I brought it up in Photoshop later!

So why exactly is verdant Madison Heights such a veritable desert for those hardy creatures that grow abundantly on every continent on the planet, from the highest to the lowest, from the wettest to the driest, from pole to pole, and can be found thriving on fully-exposed baking-hot black rocks in the middle of the Mojave Desert hardly a few hours' drive away?

Air pollution. Industrial pollution, in particular. Lichens cannot abide the high levels of sulfur dioxide and nitrous oxides in the air around urban centers. Lichens are adept at filtering and concentrating any "nutrients" they can find in the air normally a perfectly advantageous trait in environments too nutrient-poor for any other macroscopic life forms, but one that seals their doom in the unusual environment our cities create. In fact ecologists make wide use of lichens as indicators: lichens are the first to go as air quality deteriorates, the modern equivalent of parakeets in coal mines.

Spray zone at base of a magnolia. Notice the green ring of algae surrounding a central area leached clean of all nutrients (and life) by constant rinsing action of nightly sprinklers.

That's what makes Madison Heights interesting. No lichens should grow there. Yet a few manage. Look for the greenish cast at the base of trees in well-watered lawns. This is the tell-tale sign of algae growing at the edge of the spray zone of sprinklers. (Not in the spray zone, mind you, that area is leached sparkling clean.) Don't see anything? Look closer. Much closer!

Apothecia of Lecanora hagenii under 30x dissection scope.

Every so often you will find a grayish spattering of minute pin-head-sized disks. This is the amazing rim lichen Lecanora hagenii. Look it up on the web with the word "urban" or "pollution" and you will find countless reports talking about how this lichen is one of the most toxitolerant species on the planet, growing in cities throughout Europe and North America. Where other lichens are poisoned out of existence, Lecanora hagenii seems to thrive on the excess nitrogen and sulfur and the acidic conditions.

In similar locations one can find (albeit very rarely) even more minute black specks. This is another cosmopolitan species, the button lichen Amandinea punctata. It grows in much the same conditions as Lecanora hagenii, although occasionally will give granite landscaping rocks a brief try, too.

Such sterile lichens are notoriously hard to classify, since fungus classification is based on microscopic details of the fruiting bodies. Indeed, not until 1981 did anyone finally find a specimen of Chrysothrix with an apothecium! Prior to that it was lumped in with Lepraria, a genus which remains unclassified to this day.

Such sterile lichens are notoriously hard to classify, since fungus classification is based on microscopic details of the fruiting bodies. Indeed, not until 1981 did anyone finally find a specimen of Chrysothrix with an apothecium! [1] Prior to that it was lumped in with Lepraria, a genus which remains unclassified to this day. [2]

Particularly vivid and well-defined gold dust lichen, Chrysothrix?

The other species you'll stumble across, often without realizing it, are the dust lichens. In marginal habitats such as LA, they are rarely more than diffuse powdery residues in the lea of protective angles of bark or rock. They come in dingy grayish white to greenish (Lepraria lobificans) to a quite striking yellow (Chrysothrix spp.). Indeed a typical specimen of gold dust will look more like spray paint than a living thing! All these species are invariably sterile, propagating vegetatively instead via the dust. Which exact species are present in Madison Heights is almost certainly unknown, and is at any rate a matter on which I am entirely unqualified to speculate.

For those who are sufficiently inspired (and conveniently located), all but Amandinea punctata can be found growing in profusion on a number of the date palms in front of the Huntington Hospital on Calfornia Blvd. Amandinea punctata is a bit more tricky to find, although my notes from 20070622 describe a good population in San Marino on the southwest corner of Encino and Hillcrest, near the Ritz.

Citations:
1. Laundon, 1981
2. Brodo et al., 2001