ULVA DICHOTOMA. DICHOTOMOUS ULVA.
ULVA dichotoma,. fronde olivaceo-flavicante, plana, enervi, membranacea, lineari, integerrima ; se=
minibus ubique sparsis.
ULVA dichotoma. Huds. Angl. p . 568. L ig h tf. Scot. ». 2. p. 975. t. 34. With. Bot. A r r . >6. 4
p . 124. Engl. Bot. t. 774.. Lamarck Fl. Fr. cd. Si ». 2. ». 'll. Lam. FI. Gall. Syn. p. 3,
Lam. Diet. ». 8. p. 166.
FUCUS zosteroides. Lamouroux Diss. Fuc. p. 25» t. 22, f 3. et t. 23. f i.
FUCUS ceranoides, viridis. Wulfen Crypt. Aquat. no. 9- (fide sui'herbarii.)
DICTYOTA dichotoma. Lamouroux in Jtôurn. de Bot. ». 2. p. 42. Id . in Annales du Mus. d'Hist:
N a t. ». 20. p. 273. Poiret in Lam. Diet. Suppl. ». 2. p . 478.
FUCUS membranaceus, dichotomus, gramineus; R ail Sym p. 45 ?
ß . inæqualis* segmentis extremis, triplo quadruplove angustioribus quam primaria.
y. implexa ; fronde vix bipollicari, lineari, angustissima, implexa.
ULVA dichotoma. Engl. Bot. t. 774. 2. par. 2. With. Bot. A rr. ». 4.p . 124
FUCUS implexus. Desfont. A tl. ». 2. p. 423. Poiret in Encycl. Meth. ». 8. p. 400.
DICTYOTA implexa. Lamouroux in Journ. de Bot. », 2. p. 43.- Ids in Annales du Mus-. d’Hist;
N at. », 20. p. 273. Poiret in Lam. Diet. Suppl. ». 2. p. 479.
ULVA dichotoma., Clemenii,-p. S2Ö.
Class a n d Order, &c. See ULVA ATOMARIA.
Radix plane nulla, nisi surculorum plurimortim dense
intertextorum vix lineam latonim congeries, qui
repentes in novas frondes assurgunt, et hinc
Frondes gregariæ, cæspitosæque, planæ, nèrvo* venis-
que carentes, sex novem pollices longoe, et latitu-
dinein nunc duarum nunc quatuor linearum a basi'
ad apices usque servantes, plerumque ad unius al-
teriusve a radice intervallum bifurcæ, mox repetite
dichotomæ, furcarum angulis nunquam non
acutis, intervallo inter singulas dichotomias sub-
pollicari; margines ubique integerrimi, apices
emarginati, rotundati ; substantia tenera et membranacea,
ad cartilagineam tamen accedens, sub i
lente insigniter reticulata ; -color dilute oliva-
ceus, flavicante perfusus, diaphanus.
FrüCTIFICATIO : Semina atro-fusca, pro plantas ratione
majuscula, subrotunda, .limbo lato, pellucido
cincta, in ramis superioribus sparsa, nec tamen
omnino absque ordme, cum lineas longitudinales
quodammodo référant.
Root evidently none, except a congeries of many sur-
culi thickly interwoven and about a line wide
may be considered so: these, when creeping,
.arise into new fronds* and hence the
Fronds are gregarious, csespitose, plane, .without
nerves and veins, from six to nine inches long,
and from two to four lines wide from the base to
the apex* generally forked at some distance from
the root, then repeatedly dichotomous, with the
angles of the bifurcations always acute, and there
is about an inch distance between each division;
the margins every where entire, the apices emar-
ginate, rounded; the substance delicate and
membranaceous, but approaching to cartilaginous,
under a microscope remarkably, reticulated
: the colour is a pale olive, tinged with
yellow, diaphanous.
Fructification : Seeds blackish-brown, large for the
size o f the plant, roundish, bordered with a
pellucid wide limbus, scattered about on the
upper branches* scarcely however without order,
since they lie in somewhat longitudinal lines.
Fig. 1. . Segment o f the frond. Fig. 2. Seeds:—both magnified.
This plant is not uncommon on the British shores during the summer months : it is also found on the coasts of
France and Italy, and by the kindness of Sir Joseph Banks we have received specimens gathered by himself in
New Zealand. The varieties (3 and y were communicated by Mr. Stackhouse from Cornwall. The latter was
gathered by Mr. Desfontaines on the coast of Barbary; and according to Mr. Clementi, who communicated it to
Mr. Turner, it abounds in the neighbourhood of Cadiz.
The flat frond and dichotomous mode o f growth immediately distinguish this plant from all the other species of
the genus Ulva, among which its scattered naked seeds induce us to suffer it for the present to retain a place.
The first author who appears to have certainly mentioned it is Hudson, it seeming necessary to put a mark of hesitation
to the earlier synonym of Ray, because he himself expresses a doubt how far his plant is really distinct
from his No. 20, Fucus alatus. Ulva dichotoma, however, was not generally known among botaniste till the
publication of Lightfoot’s figure, which, though imperfect, is characteristic. His description is, as usual, excellent :
the reticulated structure of the frond was little likely to escape so accurate an observer, and he remarks upon it,
with his usual correctness, that the whole is finely reticulated ; the meshes nearly square, and running in longitudinal
lines contiguous to each other. That he should have been induced from this circumstance to imagine at first it
might belong to the class of Zoophytes, and be ranged in the Linnean genus Flustra, appears to us, we own a little
extraordinary. Scarcely less so is the error of Lamouroux, in referring as a synonym to Ulva dichotoma the
U. punctata of Stackhouse, which, though the two plants are wholly dissimilar in almost every respect, he does
without hesitation; and is followed in this by Poiret, but not by Decandolle. Our friend M. Desfontaines and the
late lamented Abbé von Wulfen have also fallen into a singular mistake respecting this plant : the former in considering
it possible that his F. implexus, which is certainly only a small variety of U. dichotoma, may possibly not
be distinct from F.plicatus ; the latter, in joining our Ulva with his F. ceranoides, the F. bifidus of English authors.
By the kindness of Dr. Wright of Edinburgh we many years ago received from him specimens of an Ulva gathered
by himself a t Jamaica, and in its size, colour, and mode of growth, altogether resembling U. dichotoma
but regularly crenate, with minute teeth along its margin, and under a microscope quite different in its structure!
O f this, which appears to us a curious plant, we hope before long to see a figure and description given to the
Linnean Society.