Acrochaetium sargassicola Børgesen

Acrochaetium sargassicola Boergs., sp. nov. ; A. affini Howe
et Hoyt proximum, quod tamen disco basali magis evoluto,
antheridiis alio modo formatis praecipue differì.
Thallus usque ad 2 mm. altus. Cellula basalts major, oblongo-
subcylindrica, parte basali in textura hospitis immersa ; e parte
superiore, haud immersa, fila erecta nascuntur. Fila erecta a basi
ramosa, apicem versus sensim paullum attenuata, in parte basali
8-13 lata, superne 5 ¡j. lata. Cellulae cylindricae, inferiores
18-25 if longae, superiores ad 50 (j. longae, chromatophorum parietale
pyrenoide laterali instructum complectentes. Ramificatio uberrima,
ramis sparsis, in superiore parte plus minus secundatis. Sporangia
sessilia aut pedicellata, subcylindrico-ellipsoidea, 16-19 I1 longa,
11 p. lata. Antheridia et carpogonia in ramulis brevibus plerumque
secundatim ortis nascuntur.
India : Bombay, growing socially upon Sargassum sp.,
Boergesen 5005 (type).
. 3 , ) “135___
The plant (Fig. 3) reaches a height of more than two mm. Ihe
basal cell (Fig. 4a) is oblong-subcylindrical, often a little narrowed
in the middle. The lowermost part is embedded in the tissue of the
host. It has a length of about 26-28 [i. and a breadth of 12-15 and
has thick walls. In rare cases an accessory cell is developed close to
the original basal cell (Fig. 5a). The erect filaments are from
8-13 [J. broad with cells 18-25 ¡x long. Higher up, the filaments taper
gradually and the cells are longer, about 8 ¡j. broad and 50 ¡j. long.
The tips of the filaments are about 5 ¡j. and the apical cells are rounded.
The plant is much branched above, and the branches are given off
irregularly on all sides, though with a tendency to be unilateral.
As far as can be seen from dried material (my material in spirit had
dried), the chromatophore is parietal with a large protruding
pyrenoid. The sporangia are ellipsoidal in shape ; though generally
sessile or pedicellate, some are terminal at the ends of the filaments.
The sporangia are about 11 y. thick and 16-19 P1 l°n&- The antheridia
(Fig. 4d) are developed on short unilateral or rarely opposite
116
Fig. 4. Acrochaetium sargassicolum Boergs. a, base of plant ; b, c,
branches with monosporangia ; d, branch with antheridia. (a, b, c, x 300 ;
d, X 250).
branchlets. The main filaments of the branchlets are about 50 ¡j,
long and composed of 5-6 short cells. The ramuli with antheridia
are produced on the upper side of these cells (Fig. 5c). Very few
carpogonia were seen and these were in most cases in rather poor
condition. They occur in the branchlets close to the antheridia
and have the usual lageniform shape (Fig. 5c). Monosporangia
occur on the same plant and even on the same branch as the sexual
organs (see Fig. 5b, showing branchlets with sporangia and antheridia
alternating).
Fig. 5. Acrochaetium sargassicolum Boergs. a, base of plant showing
beginning of a disc ( x 250). b, branch with monosporangia and antheridia
alternating ( X 350) ; c, branchlet with a carpogonium and antheridia (x 600).
Acrochaetium sargassicola comes near to the three related species,
A. affine Howe et Hoyt, A. robustum Boergs. and A. Hoytii Collins.
A thorough comparison of their relationship has been made by Howe
and Hoyt (see Memoirs New York Bot. Gardens, 1916, 118). Besides
117
differences in size, etc., A, robustum has a small disc, which is also
more or less developed in A. affine, but is not present in *4. Hoytii.
NEW YORK BOTANICAL GARDEN
02141542
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