NO. 1 DAWSON: MARINE RED ALGAE OF PACIFIC MEXICO 15 



Antithamnion dendroideum Smith & Hollenb. 

 PL 3, fig. 2-3; PI. 5, fig. 1 

 Smith & Hollenberg 1943, p. 217, fig. 20-21. 



Thalli to 2 cm tall, with a percurrent axis bearing two or three 

 major branches and with a simple branchlet opposite each major 

 branch; cells in lower portion of axis 100-150 p broad and with a length 

 3.5 times the breadth; basal cells of axis with long descending 

 rhizoids; axis and branches with an opposite pair (very rarely a 

 verticil of three) branchlets from the upper end of each cell; branchlets 

 usually simple, 10-14 celled, and with the terminal three or four cells 

 tapering abruptly to form an acute tip, occasionally with short pectinate 

 branchlets from the adaxial side, these very short (2-4 celled) and with 

 a gland cell, or longer and without; cells of branchlets up to 80 p broad 

 and with a length 2.5 times the breadth; tetrasporangia broadly 

 elliptical, about 60 p long, within a thick envelope, pedicellate and in 

 small adaxial groups on the long lateral branchlets or on the occasional 

 short secondary lateral branchlets; sexual plants not seen. 



Type: G. M. Smith 41-525, in the Dudley Herbarium, Stanford 

 University. 



Type locality: On a rock fragment from a depth of 30-35 ft. 

 about 14 mile northeast of the municipal pier, Monterey, Calif. 



Mexican distribution: Pacific Baja Calif. — D. 8298, Isla Guada- 

 lupe (60 m.). 



Antithamnion glanduliferum Kylin 

 PL 4, fig. 5-7 

 Kylin 1925, p. 47, fig. 28 E-G; Dawson, Neushul & Wildman 1960a, p. 24. 

 Antithamnion scrippsiana Dawson 1949, p. 15, fig. 26, 27, 58. 



Thalli 3-5 mm high (said to reach 5 cm), consisting of a group 

 of erect, sparsely branched, ± percurrent, distichous axes from a 

 common, pad-like base; main axis 30-40 p in diameter, of cells 1.5-2.0 

 diameters long, provided at each cell node with an opposite pair of 

 determinate branchlets or an indeterminate branch opposite a deter- 

 minate one (occasionally with a 3rd determinate branch at a node) ; 

 determinate branches of 8-12 cells, ascending, usually simple, terminally 

 somewhat blunt, of cells about as long as wide; gland cells apparently 

 absent in the Mexican material (occasional to frequent in southern 

 Calif ornian and more northern material) ; tetrasporangia ellipsoidal to 

 ovoidal, apparently tetrahedrally divided, about 40 p long or more, 

 adaxial and sessile on the lower 2-3 cells of the determinate laterals; 

 spermatia borne in small, contiguous clusters on short, 2-3-celled 

 spermatangia along nearly the whole adaxial surface of determinate 

 laterals. 



Type: A collection by Kylin without designation, probably in 

 the Agardh Herbarium, Lund, Sweden. 



