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The grass genera of the world

L. Watson, T.D. Macfarlane, and M.J. Dallwitz

Ptilagrostis Griseb.

From the Greek ptilo (down, as in feather) and agrostis (forage grass), alluding to pilose awns.

~ Stipa

Habit, vegetative morphology. Perennial; caespitose. Culms (5–)10–60 cm high; herbaceous; branched above, or unbranched above (?); (1–)2–3 noded. Culm nodes hairy, or glabrous (?). Culm internodes solid, or hollow (?). Young shoots intravaginal. Leaves not basally aggregated; non-auriculate. Leaf blades linear; very narrow; 0.2–0.9 mm wide (less than 0.5 mm when dry); setaceous (‘filiform’, twisting when dried); folded, or rolled; not pseudopetiolate; without cross venation; persistent; once-folded in bud. Ligule an unfringed membrane; truncate, or not truncate; 0.2–3 mm long. Contra-ligule present, or absent (?).

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets; inbreeding; exposed-cleistogamous, or chasmogamous (?); with hidden cleistogenes, or without hidden cleistogenes (?). The hidden cleistogenes (if present) in the leaf sheaths (?).

Inflorescence. Inflorescence few spikeleted to many spikeleted; paniculate; not deciduous; open, or contracted; with capillary branchlets (?); espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.

Female-fertile spikelets. Spikelets 3.4–7.5 mm long; compressed laterally; disarticulating above the glumes. Rachilla terminated by a female-fertile floret. Hairy callus present. Callus short (0.2–0.8 mm long); blunt.

Glumes two; more or less equal (subequal); slightly exceeding the spikelets, or about equalling the spikelets; long relative to the adjacent lemmas (equalling to slightly exceeding them); hairless; glabrous; pointed to not pointed (rounded, acute, or abruptly, briefly acuminate); awnless; non-carinate; similar (firmly membranous to hyaline). Lower glume (0–)1 nerved, or 3 nerved, or 5 nerved (cf. Tsvelev 1976, Freitag 1985). Upper glume (0–)1 nerved, or 3 nerved. Spikelets with female-fertile florets only; without proximal incomplete florets.

Female-fertile florets 1. Lemmas lanceolate to ovate-lanceolate; convolute to not convolute (not concealing the palea); not saccate; without a crown; decidedly firmer than the glumes; with oval to rectangular abaxial epidermal silica bodies; not becoming indurated (membranous to leathery); dark brown in fruit; incised; 2 lobed; not deeply cleft; awned. Awns 1; median; from a sinus; geniculate (or sometimes bi-geniculate); long-plumose (usually, constituting a supposed distinction from Achnatherum), or hairless to hairy (P. kingii); much longer than the body of the lemma (7–42 mm long); entered by several veins (?); persistent (and without a basal articulation). Awn bases twisted. Lemmas hairy (the pubescence diffuse, confined to the lower part, or denser there); non-carinate (terete); having the margins lying flat on the palea; without a germination flap; (1–)3(–5) nerved. Palea present; relatively long (about equalling the lemma); tightly clasped by the lemma; not prow-tipped; entire (the tip flat and rounded); awnless, without apical setae; textured like the lemma; not indurated; 2-nerved (the veins falling short of the apex); keel-less. Palea back hairy. Lodicules present; 3. Third lodicule present. Lodicules free; membranous (stipoid, the third somewhat different); ciliate (e.g. P. mongholica), or glabrous; not toothed; heavily vascularized. Stamens 3. Anthers 0.4–3.3 mm long; penicillate, or penicillate to not penicillate. Ovary apically glabrous. Styles free to their bases. Stigmas 2; white.

Fruit, embryo and seedling. Fruit free from both lemma and palea; small (1.7–3.3 mm long); linear, or fusiform; not grooved; compressed laterally. Hilum long-linear. Embryo small; not waisted. Endosperm hard; without lipid; containing only simple starch grains, or containing compound starch grains (?). Embryo with an epiblast (the epiblast short, truncate); without a scutellar tail; with a negligible mesocotyl internode. Embryonic leaf margins meeting.

Seedling with a short mesocotyl, or with a long mesocotyl (?). First seedling leaf with a well-developed lamina. The lamina narrow; erect.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous, or lacking.

Transverse section of leaf blade, physiology. C3; XyMS+. Combined sclerenchyma girders absent. Sclerenchyma all associated with vascular bundles, or not all bundle-associated. The ‘extra’ sclerenchyma of P. kingii in a continuous abaxial layer.

Cytology. Chromosome base number, x = 11. 2n = 22. 2 ploid. Chromosomes ‘medium sized’. Nucleoli disappearing before metaphase.

Classification. Watson & Dallwitz (1994): Stipoideae; Stipeae. Soreng et al. (2015): Pooideae; Stipeae. About 8 species.

Distribution, phytogeography, ecology. Eastern U.S.S.R., western China, Himalayas, western North America.

Helophytic to mesophytic (alpine-subalpine); species of open habitats. Alpine-subalpine.

Economic aspects. Important native pasture species: All the species are pasture plants.

Rusts and smuts. Rusts — Puccinia. Smuts from Tilletiaceae and from Ustilaginaceae.

References, etc. Morphological/taxonomic: Tvelev 1976; Barkworth 1983; Freitag 1985; Barkworth and Everett 1987; Barkworth 1993. Leaf anatomical: studied by us - P. neomexicana.

Special comments. A Stipa segregate containing S. kingii, S. mongholica, etc., unsatisfactorily delimited from Achnatherum. See further comments under Stipa sensu lato. Illustrations. • P. mongholica, P. purpurea, P. subsessiliflora: Fl. U.S.S.R. 2, 1934

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Cite this publication as: ‘Watson, L., Macfarlane, T.D., and Dallwitz, M.J. 1992 onwards. The grass genera of the world: descriptions, illustrations, identification, and information retrieval; including synonyms, morphology, anatomy, physiology, phytochemistry, cytology, classification, pathogens, world and local distribution, and references. Version: 11th December 2017.’.