Glyceria ×occidentalis
Glyceria maxima
northwestern manna grass, western manna grass
English watergrass, giant mannagrass, glycerie aquatique, reed manna grass, rough mannagrass, tall glyceria, tall mannagrass
60-160 cm tall, 2.5-5 mm thick, erect or decumbent and rooting from the lower nodes.
60-250 cm tall, 6-12 mm thick, erect.
smooth to scabridulous, keeled, sometimes weakly so;
ligules 7-12 mm;
blades 20-30 cm long, (2.5)4-12 mm wide, adaxial surfaces scabridulous, occasionally papillose.
scabridulous, keeled;
ligules 1.2-6 mm, rounded or with a central point, ligules of the lower leaves thick, stiff, and opaque, ligules of the upper leaves thinner and translucent;
blades 30-60 cm long, 6-20 mm wide, both surfaces smooth or adaxial surfaces scabridulous.
20-50 cm long, 2-15 cm wide, usually narrow, open at anthesis;
branches 4.5-18 cm, somewhat lax, usually ascending, strongly divergent at anthesis, with 2-8 spikelets, pedicels 1.5-8 mm.
15-45 cm long, to 30 cm wide, open;
branches 8-20 cm, lax, strongly divergent or drooping at maturity, scabridulous, primary branches with 50+ spikelets;
pedicels 0.8-10 mm.
13-23 mm long, 1.5-3.5 mm wide, cylindrical and terete, except at anthesis when slightly laterally compressed, rectangular in side view, with 6-13 florets.
5-12 mm long, 2-3.5 mm wide, somewhat laterally compressed, oval in side view, with 4-10 florets.
acute to obtuse;
lower glumes 1.1-2.8 mm;
upper glumes 2.9-3.7 mm, about twice as long as the lower glumes;
rachilla internodes 1-2.8 mm;
lemmas 4.5-5.9 mm, scabridulous, midveins extending to within 0.1 mm of the apical margins, apices acute, usually slightly lobed or irregularly crenate;
paleas usually shorter than or equaling the lemmas, sometimes slightly longer, keels winged, apices shallowly notched to slightly bifid, teeth to 0.2 mm, parallel;
anthers 2, 0.6-1.6 mm.
unequal, usually the midvein of 1 or both reaching to the apices;
lower glumes 2-3 mm;
upper glumes 3-4 mm, longer than wide;
rachilla internodes 0.5-1 mm;
lemmas 3-4 mm, 7-veined, veins scabridulous, apices broadly acute to rounded, slightly prow-shaped;
paleas subequal to the lemmas, lengths more than 3 times widths, keels not winged, ciliate, tips not strongly incurved, curved to broadly notched between the keels;
anthers 3, (1)1.2-2 mm.
1.5-2 mm.
= 40.
= 60.
Glyceria ×occidentalis
Glyceria maxima
Glyceria ×occidentalis has hitherto been considered an uncommon native species that grows along lakes, ponds, and streams, and in marshy areas of western North America. It differs from other species in the region primarily in its longer lemmas and anthers. Studies of chloroplast DNA in western North American species of Glyceria demonstrated that, contrary to C.L. Hitchcock's (1969) conclusion, G. fluitans is present in western North America, and that all specimens being identified as G. ×occidentalis had cpDNA resembling that of G. leptostachya or G. fluitans; there was no distinctive G. ×occidentalis cpDNA (Whipple et al. [in press]). This strongly suggests that G. ×occidentalis is a series of reciprocal hybids, and probably backcrosses, between G. fluitans and G. leptostachya. As the key indicates, G. ×occidentalis is intermediate between its two putative parents. The cpDNA study also confirmed that G. declinata is distinct from G. ×occidentalis (see discussion under that species).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Glyceria maxima is native to Eurasia. It grows in wet areas, including shallow water, at scattered locations in the flora region. It is an excellent fodder grass, and may have been planted deliberately at one time (Dore and McNeill 1980). At some sites, the species appears to be spreading, largely vegetatively. It is easily confused with large specimens of G. grandis, but differs in its firmer, more prow-tipped lemmas as well as its larger lemmas and usually larger anthers.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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