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821
ON A NEW HYBRID POTAMOGETON OF THE
FLUITANS GROUP.
By Alfked Fkyer.
(Plate 2Q9.)
Potamogeton crassifolius milii = P. Zizii x P. natmis.—
Rootstuck with thick stolons, rooting deeply in the soil ; stem 4-5 ft.
long, very stout, round, simple below, branched above with simple
branches ; leaves all stulked, corideeoits, opaque ivhen mature ; lower
leaves reduced to submerged phyllodes, or narrowly lanceolate and
tapering into the petiole, or with a distinct lanceolate lamina, all
thick and coriaceous like the %(p}ier ones ; distant, few in number,
usuallu all decayed by the time of jloweriny ; upper leaves very thick and
fleshy, oblong-elliptical, or oval, with a i^ronnnent fold at the base of
the lamina, which is slightly decurrent, or rarely lanceolate and
gradually narrowed into the stalk; petiole flat above, slightly enlarged
towards the apex, shorter than the lamina ; stipules not winged, not
channelled on the back, but with two conspicuous green ribs, horny
with scarious edges, or herbaceous, acute; lowest sometimes bearing
a short phyllode, or more rarely a long lanceolate ordinary lower
leaf ; peduncles of equal thickness throuyhout, terminal becoming
lateral by growth of the branch, equalling or slightly exceeding the
stem in thickness, 2-3 times as long as the Hower- spike, much
shorter than the subtending leaves ; flower-spike cylindrical, dense,
1-1:^ in. long, usually (always?) barren, perianth-leaves closed at
the time of flowering, but the stigmas exserted ; colour of the whole
plant briykt yreen, or with the young upper leaves sometimes reJdish
or streaked with reddish purple.
Potamoyeton crassifolius differs in its parentage from P. jluitans
Roth, l)eing a hybrid between forms of P. Zizii and /'. nutans,
instead of between P. luccns and P. nutans. It varies slightly
from the type described above, because in different localities it originates
from different forms of [\ Zizii, and because the seed-parent
is sometimes Zizii and sometimes natuns. The type of the species
(figured PL 299) is a very robust plant, growing in deep water, and,
altliough springing from a single rootstock, spreading along the
water for a distance of 10 or 12 yards. In habit and general
appearance it closely resembles a large form of P. Zizii [P. cori((ceus
V. major mihi), which grows in the same drain intermixed with
/'. niitaus, and probably it is coriureus J x natuns 3- . The
upper
floating-loaves of corinceus v. major and crassifolius so closely resemble
one another in some specimens that the plants are with difficulty
separable, except by examination of the widely different lower
leaves. In the Rlepal Engine Drain, where three separate stations
have been found, /'. crussilolius is always accompanied by P. Zizii,
and I have met witli it in no locality where that species does not
exist. In anotlier locality,—at Westmoor, in the parish of Doddujgton,—some
miles distant from tlie Mcpal station, no doubt
ab(jut its parentage is possible, as only P. Zizii and I', nutans are
Journal of Botany.—Vol. 28. [November, 1890.] y