UC specimens and range limits for Gelidium arborescens

• Blue markers: specimen records
• Yellow marker: type locality, if present
• Red markers: endpoints of range from literature

View map from the Consortium of Pacific Northwest Herbaria

Search Sequences in GenBank

Gelidium Lamouroux 1813

Thalli cartilaginous, to 30+ cm tall. Axes erect, terete to compressed, variously branched, sometimes strikingly distichous, red to deep purple or black. Plants saxicolous, attached to substratum by branched prostrate axes; proportions of prostrate and erect axes varying; plants sometimes occurring in mats of algal turf with extensive basal parts or in more discrete clumps with 1 or more axes arising from limited basal system. Cortex with several rows of pigmented cells, the smaller toward the outside, mostly 2-12 µm diam., irregularly arranged. Medullary cells in cross section generally rounded, 20-27 µm diam., colorless, compacted or loosely appressed, with or without evident starch granules. Rhizoidal filaments thick-walled, 2-5 µm diam., in medulla and/or cortex, varying in number and position within species and even within single plant. Tetrasporangia in sori at apices of branches, or extending over entire flattened lateral branchlet, or also extending into supporting branch beneath; tetrasporangial branchlets with or without distinct sterile margins; tetrasporangial plants often recognizable by dark, granular appearance of fertile branchlets, this resulting from size and intense pigmentation of spores. Spermatangial sori sometimes ap parent as relatively unpigmented areas on apices of branchlets, usually conspicuous by presence of sterile darker margin. Carpogonial filament unicellular, fusing with adjacent cells after fertilization. Mature cystocarps protruding equally on both surfaces of branch, usually with single pore on each surface, rarely with 2 or 3; vegetative growth continuing apically be yond developing cystocarp, making its position more proximal.

The following are known only from the type collections from Calif., and their relationships cannot be ascertained; for the present they must be thought of as doubtful species: Gelidium contortum Loomis (1960), San Francisco; G. umbricolum Dawson & Neushul (1966), Anacapa I.; and G. venturianum Dawson (1958), Ventura Co.

Gelidium arborescens Gardn.

Gardner 1927b: 276; Smith 1944: 197.

Thalli 8-15(25) cm tall, the branching sparse and irregular throughout, infrequently more regularly alternate and geniculate; axes cylindrical to compressed, 0.5-1.5 mm broad, 0.4-1.5 mm thick; fertile plants unknown.

Common, saxicolous, low intertidal to subtidal (3 m) at Pebble Beach (Monterey Co.), Calif., and in nearby drift. Type locality: Carmel Bay, Calif.

These plants are separable from G. purpurascens only by the sparse irregular branching. Pebble Beach is the site of plants showing branching more typical of G. purpurascens; but since several algal genera exhibit markedly different forms in this bay, and since the physical parameters of the area are quite different from more exposed areas, ecological factors ought to be considered before the status of G. arborescens is further assessed. See also discussion under G. nudifrons.

Excerpt from Abbott, I. A., & Hollenberg, G. J. (1976). Marine algae of California. Stanford University Press, Stanford, California. xii [xiii] + 827 pp., 701 figs.