Alsia Sullivant, 1855.

Normally developed forms of Alsia are easily recognized by the combination of the numerous quadrate and thick-walled alar cells, the weft growth form and the abundant foliose paraphyllia. Some confusion may come from the great variability of the costa strength on leaves from even a single clone. The costa may sometimes end significantly below the leaf middle, and it may sometimes extend even to 3/4.

Close to the ocean shore, and especially on offshore islands, Alsia may be very different from the "normal form." In such sites it grows as prostrate and sparingly to irregularly branched mats. We consider this coastal expression a form unworthy of special recognition because of similar leaf and paraphyllial morphology. High in the canopy of coastal trees of Pseudotsuga, Alsia often shows a form with short upright axes and closely arranged branches. The paraphyllia of this expression are so much more narrow than those of the typical form that Manuel (1974) annotated a specimen at UC to be taxonomically distinct. We have, with hesitancy, decided to avoid separate species recognition.

Dendroalsia is allied to Alsia but the single species of Dendroalsia has prorate-papillose median laminal cells; it is taller, mostly above 4 cm. The regularly 5-ranked leaves of Dendroalsia may be the easiest field character of distinction of a small and poorly developed specimen. Generally, however, Dendroalsia is pinnate.

Alsia has one of the more difficult-to-explain geographic and ecological ranges. It reaches its most prolific development in coastal Alnus forests in the far northwest corner of the state but it virtually disappears from the forests north of the state line. Alsia grows on coastal sites in the far northwest of the state, and it is completely replaced by Dendroalsia inland of the first ridges of the coastal mountains. A recent collection of Alsia from Yuba County seems to be a remarkable disjunct population in the extreme northwest of the Sierra Nevada. In central and southern California, Alsia is the more common plant even east of the coastal mountains with Dendroalsia perhaps more common nearest the coast.
see key to Antitrichia Etc.

Species included:
Alsia californica (W. J. Hooker & Arnott) Sullivant