The grass genera of the world
~ Poa (P. scaberula)
Habit, vegetative morphology. Short-lived perennial, or annual; caespitose. Culms 20–40 cm high; herbaceous; unbranched above. Culm nodes glabrous. Plants unarmed. Young shoots intravaginal. Leaves not basally aggregated; non-auriculate. Sheath margins joined (over the lower quarter), or free. Sheaths weakly keeled to terete. Leaf blades linear; narrow (the median vascular bundle with an adaxial groove on either side); to 3 mm wide; flat (except towards the tip); without cross venation; persistent. Ligule an unfringed membrane; not truncate; 2 mm long. Contra-ligule absent.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence paniculate; open (dense, lobed-cylindrical); espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; shortly pedicellate.
Female-fertile spikelets. Spikelets 4–5 mm long; compressed laterally; disarticulating above the glumes; disarticulating between the florets; with conventional internode spacings (or these slightly elongated). Rachilla prolonged beyond the uppermost female-fertile floret; hairless. Hairy callus usually present (small, with one or three tufts of long, fine, webby hairs more than 0.5 mm long), or absent (callus rarely glabrous). Callus short; blunt.
Glumes present; two; relatively large; more or less equal; shorter than the adjacent lemmas; hairy (scabrid-hairy on the keels); pointed; awnless; carinate. Lower glume longer than half length of lowest lemma; 1 nerved. Upper glume distinctly saccate (?); 3 nerved. Spikelets with incomplete florets (some of them). The incomplete florets distal to the female-fertile florets.
Female-fertile florets 2–3. Lemmas similar in texture to the glumes; not becoming indurated; entire; pointed; awnless; hairy (usually sparsely pubescent), or hairless (rarely glabrous); strongly carinate (naviculate); without a germination flap; strongly to obscurely 5 nerved. Palea present; conspicuous but relatively short (about two-thirds lemma length); apically notched; awnless, without apical setae; not indurated (hyaline); 2-nerved; 2-keeled. Palea keels scabrous. Lodicules present; 2; membranous; glabrous; toothed; not or scarcely vascularized. Stamens 3. Anthers 0.3–0.5; not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases. Stigmas 2.
Fruit, embryo and seedling. Fruit small. Hilum short. Pericarp free. Embryo small. Endosperm liquid in the mature fruit (probably), or hard (?).
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Mid-intercostal long-cells fusiform; having straight or only gently undulating walls. Microhairs absent. Stomata common. Subsidiaries parallel-sided. Guard-cells overlapped by the interstomatals. Intercostal short-cells absent or very rare. Costal prickles abundant. Crown cells absent. Costal short-cells neither distinctly grouped into long rows nor predominantly paired (mostly solitary, a few short rows). Costal silica bodies horizontally-elongated crenate/sinuous (mostly crenate).
Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll without adaxial palisade. Midrib with one bundle only. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (but some small bundles with strands only). Sclerenchyma all associated with vascular bundles.
Classification. Watson & Dallwitz (1994): Pooideae; Poodae; Poeae. Soreng et al. (2015): cf. Pooideae (as a synonym?); Poodae; Poeae; Poinae. 2–3 species.
Distribution, phytogeography, ecology. Highlands of central Mexico and Guatemala, Andean and Chile-Patagonian regions of South America, and Tierra del Fuego.
References, etc. Morphological/taxonomic: Soreng (1998) regards the type species, Dasypoa tenuis, as morphologically indistinguishable from Poa. Possible distinguishing features of Dasypoa presented in the present description, involving habit (leaves not basally aggregated), upper glume shape (saccate), pericarp (free) and endosperm constitution (possibly liquid) are not mentioned by him, and may well be spurious. He refers Poa conglomerata Ruprecht ex Peyritsch, P. parvicepsHackel and P. scaberula Hook f. (= P. conglomerata) to Poa sect. Dasypoa. Leaf anatomical: this project.
We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, and classifications. See also Guidelines for using data taken from Web publications.
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: 13th November 2017. delta-intkey.com/grass’.