visitors of Yosemite National Park and Sequoia National Park. They form dark vertical drip-like stripings along drainage tracks in the rock faces, resulting in Native Americans giving the name "Face of a Young Woman Stained with Tears" to Half Dome. Their tight adherence to the rocks give them the appearance of being "painted" on, and up close they appear as intricate multicolored patchwork mosaics. They often completely cover the exposed surface of the rock. They add to rock weathering. These crustose rock lichens lack rhizenes and a lower cortex (lichen). The dark vertical stains along the drainage tracks are either mosses, or of four color types of lichen, each with a slightly different color. Appearing black from a distance, but brown up close, is the abundant Lecidea atrobrunnea. Also abundant in these black-from-a-distance stripes are Dimelaena thysanota and dark gray Rhizocarpon species. More gray appearing vertical stripes have Aspecilia species and Koerberia sonomensis as major components. Staurothele areolata and other species of Staurothele and Verrucaria appear dark brown closer up. The blackest of the black are likely Nostoc species, containing cyanobacteria. Mixed in are green to dark green stripes that contain mosses. Nitrophilic (nitrogen loving) yellow Candelariella species can be found on rocks where birds perch and drop their high nitrogen containing waste products, as well as in drainage cracks with higher than normal nitrogen loads. Fruticose lichens Wolf lichens Wolf lichens in the genus Letharia are the most conspicuous in the Sierra parks because of their brilliant fluorescent yellow or chartreuse coloration. They are typified by Letharia vulpina (vulpina derives from "fox", not wolf). They are mostly absent at lower elevations, and can then be found on conifer trunks and branches, sometimes completely covering them. Letharia is the only abundant fruticose lichen in the Sierran parks, and composes the bulk of the biomass in Sequoia groves, and many other types of groves. Estimates have Letharia species as contributing from 50% to 95% of the total macrolichen biomass in some stands. It contains toxins (e.g., vulpinic acid) to many herbivores and microbes, although there are mixed reports on actual consumption. It is the vulpinic acid that gives it the brilliant yellow color. Pin lichens (calicoid lichens) Pin lichens, or calicoid lichens, are lichens with a crustose thallus and tiny fruiting bodies with stalks that resemble the head of a pin, whereby the name "pin lichen". Ecological interactions About 20 Sierra