FNA: Glyceria ×occidentalis vs. Poaceae tribe Meliceae

Distribution

CA; ID; NV; OR; WA; BC

Discussion

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.)

There are approximately 130 species and 8 or 9 genera in the Meliceae. Four of the genera are monotypic. Melica and Glyceria, the two largest genera, are well represented in North America. Pleuropogon and Schizachne are primarily North American, but extend into eastern Asia.

Molecular studies (e.g., Soreng and Davis 2000; Grass Phylogeny Working Group 2001) show the tribe to be monophyletic and somewhat basal within the Pooideae. Members of the tribe are most easily recognized by the combination of closed leaf sheaths, scarious lemma apices, and non-converging lemma veins. The tribe also differs from other tribes in the Pooideae in having 2 unwinged lodicules that are usually connate into a single structure, and a base chromosome number of 9 or 10. Catabrosa and Briza, whose inclusion in the tribe was suggested by the preliminary results of Mejia-Saules and Bisby (2000), have more membranous lemma margins and free, winged lodicules. Briza also has open leaf sheaths and more convergent lemma veins. Their inclusion is not supported by the molecular data.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Key

1. Calluses hairy; lemmas awned, awns 8-15 mm long, twisted, divergent to slightly geniculate	Schizachne
1. Calluses glabrous; lemmas unawned or awned, awns to 12 mm long, straight.	→ 2
2. Inflorescences racemes; palea keels winged, the wings notched and awned	Pleuropogon
2. Inflorescences usually panicles, racemes in depauperate specimens; palea keels not winged or the wings entire and unawned.	→ 3
3. Lower glumes 1-veined, 0.3-4.5 mm long; disarticulation always above the glumes; lemmas unawned, never with hairs more than 1 mm long; culms never with cormous bases; distal florets in the spikelets sometimes reduced, not forming a morphologically distinct rudiment; plants of wet meadows and streamsides	Glyceria
3. Lower glumes 1-9-veined, 2-16 mm long; disarticulation above or below the glumes; lemmas sometimes awned, sometimes with hairs longer than 1 mm; culms sometimes with cormous bases; distal florets in the spikelets often forming a morphologically distinct rudiment; plants of drier or well drained habitats	Melica