Acrochaetium radiatum C. C. Jao

Acrochaetium radiatum, sp. nov.
(PI. 10, figs. 18-25)
Thallo epiphytico, prostrato, ferme orbiculato vel irreguläre, altitudine ad
320/t; spora germinante in duas cellulas plus minusve aequales divisa, ex
quibus 3-6 (raro ultra) fila ramosa repentes procreantibus, plus minusve radia-
tis compositibus; filis abunde ramosis, ramulis ad media pars thalli plerumque
oppositis et dense compositis, forma pseudo-parenchymaticis, ramulis ad
apicem filiorum plerumque furcatis vel secundis et fluxis; cellulis 5.0—6.5ju altis,
6.5-9.5/i	longis; ramulis erectis non visis vel tenuiter procreantibus, solum
1- vel 3-cellularibus; chromatophoro parietali, pyrenoideo centrali; pilis ter-
minalibus, plerumque in filis erectis; monosporangiis in filis prostratis,
singulis et sessilibus, raro 1 vel 2 in filis erectis terminalibus, ovatis, (5-)
6.5-8.0¡1	altis, 8.0-9.5/i longis.
Plants epiphytic, prostrate on the host, almost circular in form or irregu-
lar, up to 320ii broad; the germinating spore dividing into two nearly equal
cells, from which are produced 3-6 (or rarely more) main filaments in all di-
rections in a single plane, resulting in a more or less regularly radiate arrange-
ment of the filaments; abundantly branched, the branches near the center
usually opposite and densely arranged, resulting in a pseudo-parenchymatous
appearance, the branches near the end of the main filaments often dichoto-
mous or secund and loose, their cells 5.0-6.5/i diameter, 6.5-9.5/i long; erect
branches absent or poorly developed, only 1-3 cells long; chromalophore
parietal, with a central pyrenoid; hairs terminal, mostly on erect filaments;
1936]	JAO: RIIODOPHYCEAE	247
monosporangia directly produced on the prostrate filaments, or sometimes 1
or 2 terminal on the erect branches, oval in form, (5-) 6.5-8.0/i diameter,
8.0-9.5,u long.
These plants bear some characteristics of Acrochaetium reduclum
(Rosen vinge) Hamel, A. humile (Rosen vinge) B^rgesen and A. pule helium
B^rgesen, but differ from them chiefly in having more than two main
filaments arising from the divided germinating spore and all the filaments
arranged radiately and densely from the center of a fully developed thallus.
Beside these characteristics, this new species is separated from the last
two especially by the absence of stellate chromatophores. Acrochaetium
maculum (Rosenvinge) Hamel also has a circular frond which is composed
of more or less regularly radiating filaments and is pseudo-parenchymatous
in appearance, but it has stellate chromatophores and a different method of
spore germination.
Found on Polysiphonia fibrillosa Grev., together with several other
species of Acrochaetium, Norton Point, Marthas Vineyard, Massachusetts,
Aug. 3, 1934. Type in C.-C. Jao collections and Herb. Univ. Mich., Woods
Hole No. 280.
'f&XL Figs. 18-25. Acrochaetium radiatum Jao, sp. nov. X605. Figures 18-23, develop-
mental stage of young plants; figures 24-25, two adult plants.
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NEW YORK BOTANICAL GARDEN
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