Piptatherum micranthum |
Poaceae tribe Stipeae |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
little-seed mountain-rice grass, littleseed ricegrass, piptatherum micranthum, small-flower piptatherum |
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Habit | Plants loosely cespitose, not rhizomatous. | Plants usually perennial; usually tightly to loosely cespitose, sometimes rhizomatous. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Culms | 20-85 cm, glabrous; basal branching extravaginal. |
annual or perennial, not woody, branches 1 to many at the upper nodes. |
||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Leaves | basally concentrated; sheaths glabrous; ligules 0.4-1.5(2.5) mm, truncate; blades 5-16 cm long, 0.5-2.5 mm wide, usually involute. |
basally concentrated to evenly distributed; sheaths open, margins not fused, sometimes ciliate distally, basal sheaths sometimes concealing axillary panicles (cleistogenes), sometimes wider than the blade; collars sometimes with tufts of hair at the sides extending to the top of the sheaths; auricles absent; ligules scarious, often ciliate, cilia usually shorter than the base, ligules of the lower and upper cauline leaves sometimes differing in size and vestiture; pseudopetioles absent; blades linear to narrowly lanceolate, venation parallel, cross venation not evident, cross sections non-Kranz, without arm or fusoid cells; epidermes of adaxial surfaces sometimes with unicellular microhairs, cells not papillate. |
||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Panicles | 5-20 cm, lower nodes with 1-3 branches; branches 2-6 cm, divergent to reflexed at maturity, with 3-10(15) spikelets, secondary branches appressed to the primary branches. |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Inflorescences | usually terminal panicles, occasionally reduced to racemes in depauperate plants, sometimes 2-3 panicles developing from the highest cauline node. |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Spikelets | usually with 1 floret, sometimes with 2-6 florets, laterally compressed to terete; rachillas not prolonged beyond the base of the floret in spikelets with 1 floret, prolonged beyond the base of the distal floret in spikelets with 2-6 florets, prolongation hairy, hairs 2-3 mm; disarticulation above the glumes and beneath the florets. |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Glumes | 2.5-3.5 mm, acute; lower glumes 1(3)-veined; upper glumes 3-veined; florets 1.5-2.5 mm, dorsally compressed; calluses 0.1-0.2 mm, glabrous or sparsely hairy, disarticulation scars circular; lemmas usually glabrous, sometimes sparsely pubescent, brownish, shiny, 5-veined, margins not overlapping at maturity; awns 4-8 mm, straight or almost so, caducous; anthers 0.6-1.2 mm, not penicillate; ovaries truncate to rounded, bearing 2 separate styles. |
usually exceeding the floret(s), always longer than 1/4 the length of the adjacent floret, 1-10-veined, narrowly lanceolate to ovate, hyaline or membranous, flexible; florets usually terete, sometimes laterally or dorsally compressed; calluses usually well-developed, rounded or blunt to sharply pointed, often antrorsely strigose; lemmas lanceolate, rectangular, or ovate, membranous to coriaceous or indurate, 3-5-veined, veins inconspicuous, apices entire, bilobed, or bifid, awned, lemma-awn junction usually conspicuous, awns 0.3-30 cm, not branched, usually terminal and centric or eccentric, sometimes subterminal, caducous to persistent, not or once- to twice-geniculate, if geniculate, proximal segment(s) twisted, distal segment straight, flexuous, or curled, not or scarcely twisted; lodicules 2 or 3; anthers 1 or 3, sometimes differing in length within a floret; ovaries glabrous throughout or pubescent distally; styles 2(3-4)-branched. |
||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Caryopses | about 1.2 mm long, about 0.8 mm wide; hila linear, 3/4 - 9/10 as long as the caryopses. |
ovoid to fusiform, not beaked, pericarp thin; hila linear; embryos less than 1/3 the length of the caryopses. |
||||||||||||||||||||||||||||||||||||||||||||||||||||||||
x | = 7, 8, 10, 11, 12. |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||
2n | = 22. |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Piptatherum micranthum |
Poaceae tribe Stipeae |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Distribution | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Discussion | Piptatherum micranthum grows on gravel benches, rocky slopes, and creek banks, from British Columbia to Manitoba and south to Arizona, New Mexico, and western Texas. The combination of small, dorsally compressed florets and appressed pedicels distinguishes this species from all other native North American Stipeae. Achnatherum contractum is the fertile derivative of hybridization between Piptatherum micranthum and A. hymenoides. It is placed in Achnatherum because it resembles that genus more than Piptatherum. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
The tribe Stipeae includes about 15 genera and approximately 500 species. It grows in Africa, Australia, South and North America, and Eurasia. In Australia, South America, and Asia, it is often the dominant grass tribe over substantial areas. It is not present in southern India, and is represented by only one native species in southern Africa. Most species grow in arid or seasonally arid, temperate regions. Morphological considerations have led to the Stipeae being placed in three different subfamilies (Pooideae, Bambusoideae, and Arundinoideae) in the past, and even to recognition as a subfamily. Molecular data support its treatment as an early diverging lineage within the Pooideae (Soreng and Davis 1998; Grass Phylogeny Working Group 2001) that is more closely related to the Meliceae than the core pooid tribes. Decker (1964) suggested including Ampelodesmos in the Stipeae on the basis of the cross sectional anatomy of its leaf blades. His suggestion is supported, not always strongly, by molecular studies (Soreng and Davis 1998; Grass Phylogeny Working Group 2001; Jacobs et al. 2006). The usual alternative is to treat Ampelodesmos as the only genus of a closely related, monospecific tribe, the Ampelodesmeae (Conert) Tutin, because it is so distinct from other members of the Stipeae, being, for example, the only member of the tribe with more than 1 floret in its spikelets and rachillas that are prolonged beyond the base of the terminal floret in a spikelet. The lowest chromosome number known in the Stipeae is 2n =18 (Prokudin et al. 1977), suggesting that all members of the tribe are ancient polyploids. The wide range of base numbers listed is based on numbers for the various genera. The primary basic chromosome number for the tribe is probably 5 or 6, with higher numbers reflecting ancient euploidy. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Key |
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Source | FNA vol. 24, p. 148. | FNA vol. 24, p. 109. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Parent taxa | Poaceae > subfam. Pooideae > tribe Stipeae > Piptatherum | Poaceae > subfam. Pooideae | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Sibling taxa | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Subordinate taxa | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Synonyms | Oryzopsis micrantha | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Name authority | (Trin. & Rupr.) Barkworth | Dumort. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Web links |