About Ptilidium californicum (Austin) Underw. & O.F.Cook
Ptilidium californicum (Austin) Underw. & O.F.Cook is a dioicous liverwort species. Individuals are small but medium-sized for a liverwort, with color ranging from golden-green to golden, though they are more typically reddish-brown, dilute purplish-red, or coppery red. These plants form dense fuzzy mats that grow in either small or large patches. Shoots measure less than 1½ mm wide. Its leaves are incubous, meaning they are decurrent on the dorsal stem surface, and are deeply bilobed; each lobe divides 1 to 3 times, is elongated and narrowly lanceolate, and is deeply divided. Lobe margins are entire, with 1 or 2 long, slender cilia-like projections along the margins and at lobe apices. Leaves are so closely overlapping that only a mass of ciliate projections is visible when viewed through a hand lens. Underleaves are prominent, wider than the stem, about half the size of the main leaves or smaller, 2 to 3 clefted, and have ciliate margins that are even more finely divided into slender projections. Frequent perianths are plicate and narrowed toward a ciliate mouth. Abundant sporophytes develop from May to August. For field identification, the many leaf lobes divided into slender cilia make this species unmistakable. While it was previously reported to grow in Russia and Japan, recent literature classifies this species as endemic to the west coast of North America, where its range stretches from southeastern Alaska to northern California. This species has narrow environmental requirements; it grows in old-growth forest and acts as an indicator species for this habitat. It is typically epiphytic, growing on bark at the base of standing mature to old-growth trees including Abies concolor, A. magnifica, and Pseudotsuga menziesii, or on recently fallen logs. It grows rarely on other organic substrates, such as decaying logs and stumps, or humus that covers boulders. At the southern end of its range in Oregon and California, this species is distinctly restricted to middle elevation forests. Its overall elevational range is 389–1,745 m, or 1,275–5,725 feet. The fire ecology of this plant is not currently studied, but fires in old-growth habitat may negatively impact P. californicum via smoke damage or excessive canopy opening. Severe fires that destroy old-growth trees would likely extirpate local populations of this species.
