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The grass genera of the world

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

Libyella Pamp.

~ Poa

Habit, vegetative morphology. Diminutive annual; caespitose. Culms 2–5 cm high, or 0 cm high (the internodes reduced); herbaceous. Leaves mostly basal; non-auriculate. Sheath margins joined. Leaf blades linear to linear-lanceolate; narrow; 0.4–1 mm wide; folded; without cross venation; persistent. Ligule present (its margins connate); an unfringed membrane; not truncate; 0.5–1 mm long. Contra-ligule absent.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; hermaphrodite and female-only, or hermaphrodite, female-only, and male-only (the lowest spikelet of the terminal inflorescence female and hidden in the uppermost sheath, the rest hermaphrodite or rarely male). The male and female-fertile spikelets segregated, in different parts of the same inflorescence branch (the lowest spikelet of the inflorescence, hidden in the uppermost leaf sheath, being female). Plants with hidden cleistogenes. The hidden cleistogenes in the leaf sheaths and subterranean (in the radical leaf sheaths: solitary, lacking glumes, with stigmas up to 25 mm long projecting from the sheaths).

Inflorescence. Inflorescence few spikeleted; a single spike. Inflorescence with axes ending in spikelets. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary; not secund; sessile to subsessile (occasionally), or pedicellate; not imbricate.

Female-fertile spikelets. Spikelets 3–4 mm long; compressed laterally; disarticulating above the glumes. Rachilla terminated by a female-fertile floret. Hairy callus absent.

Glumes one per spikelet (in the hermaphrodite/male spikelets), or two (in the single female spikelet); very small, scarious; very unequal to more or less equal; shorter than the spikelets; shorter than the adjacent lemmas; lateral to the rachis; hairless; glabrous; not pointed; awnless; non-carinate; similar. Lower glume 0 nerved, or 1 nerved. Upper glume 0 nerved, or 1 nerved. Spikelets with female-fertile florets only.

Female-fertile florets 1 (but cleistogamous spikelets of L. cyrenaica may have two). Lemmas lanceolate; similar in texture to the glumes (scarious); not becoming indurated; more or less incised; not deeply cleft (irregularly serrate or erose); awnless; hairy (shortly villous on the lower half); carinate; without a germination flap; 5 nerved (though the laterals may be very short). Palea present; relatively long; irregularly serrate or erose; awnless, without apical setae; textured like the lemma; not indurated; 2-nerved; 2-keeled. Palea back hairy. Palea keels wingless; hairy. Lodicules present, or absent; when present, 2; free; membranous; glabrous; toothed; not or scarcely vascularized. Stamens 3. Ovary apically glabrous. Styles free to their bases. Stigmas 2.

Fruit, embryo and seedling. Fruit free from both lemma and palea; small (1.4–2.5 mm long); compressed laterally. Hilum short. Embryo small. Endosperm hard; containing compound starch grains. Embryo with an epiblast; without a scutellar tail; with a negligible mesocotyl internode. Embryonic leaf margins meeting.

Abaxial leaf blade epidermis. Costal/intercostal zonation lacking. Papillae absent. Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally (rather thick walled). Intercostal zones with typical long-cells. Mid-intercostal long-cells fusiform (these, and all the long-cells); having straight or only gently undulating walls. Microhairs absent. Stomata fairly common. Subsidiaries non-papillate; parallel-sided. Guard-cells conspicuously overlapped by the interstomatals. Intercostal short-cells absent or very rare. No prickles or macrohairs seen. Costal zones without short-cells. Costal silica bodies absent.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma; without adaxial palisade. Midrib fairly conspicuous (via the large bundle and a fairly prominent adaxial rib); with one bundle only (this being the only primary bundle in the blade). The lamina symmetrical on either side of the midrib. Bulliforms seemingly not present in discrete, regular adaxial groups. Many of the smallest vascular bundles unaccompanied by sclerenchyma (the blade apparently lacking bundle-associated sclerenchyma). Combined sclerenchyma girders absent. Sclerenchyma confined to a tiny group in each blade margin.

Classification. Watson & Dallwitz (1994): Pooideae; Poodae; Aveneae. Soreng et al. (2015): Pooideae; Poodae; Poeae; Poinae. 1 species (L. cyrenaica).

Distribution, phytogeography, ecology. Libya, Morocco.

In coastal sandy places.

References, etc. Leaf anatomical: studied by us.

Illustrations. • L. cyrenaica: Pampanini, Bull. Soc. Bot. Italiana (1922)

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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.’.