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The grass genera of the world

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

Pleiadelphia Stapf

~ Elymandra (E. gossweileri)

Habit, vegetative morphology. Annual. Culms 80–190 cm high; herbaceous; branched above. Culm nodes glabrous. Culm leaves present. Plants unarmed. Leaves not basally aggregated; with tough, auricle-like extensions of the sheath along the sides of the ligule. Leaf blades linear (attenuated); narrow; 1–4 mm wide (and up to 30 cm long, scabrid above and on the margins); setaceous-tipped; without cross venation; persistent. Ligule an unfringed membrane; truncate; about 0.5 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 sterile; overtly heteromorphic (only the fertile spikelet awned); in both homogamous and heterogamous combinations (the raceme with 1–4 basal, homogamous sterile pairs and a terminal heterogamous triad). Plants inbreeding (seemingly, the ‘racemes’ enclosed in the spatheoles); exposed-cleistogamous (?).

Inflorescence. Inflorescence paniculate; open; spatheate; a complex of ‘partial inflorescences’ and intervening foliar organs. Spikelet-bearing axes ‘racemes’ and very much reduced (reduced to 1–4 basal homogamous pairs and the terminal triad); solitary (one per spatheole); disarticulating; disarticulating at the joints (i.e. at the only joint). ‘Articles’ linear; without a basal callus-knob; not appendaged; disarticulating obliquely. Spikelets in triplets (with a terminal triad), or paired (below); sessile and pedicellate; consistently in ‘long-and-short’ combinations; in pedicellate/sessile combinations. Pedicels of the ‘pedicellate’ spikelets free of the rachis. The ‘shorter’ spikelets hermaphrodite (in the terminal triad). The ‘longer’ spikelets sterile.

Female-sterile spikelets. The sterile spikelets awnless, tending not to disarticulate. The lemmas awnless.

Female-fertile spikelets. Spikelets (12–)14–16 mm long; not noticeably compressed to compressed dorsiventrally; falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus present (densely bearded). The callus hairs brown (fulvous). Callus long; pointed.

Glumes two; more or less equal; long relative to the adjacent lemmas; at least the G1 hairy; without conspicuous tufts or rows of hairs; awned (G2); non-carinate; very dissimilar (the G1 leathery, obtuse or truncate and awnless, the G2 thinner, truncate to emarginate with a long slender awn, weakly impressed by the margins of G1). Lower glume 2-grooved to accommodate the pedicels of the sterile spikelets; convex on the back; not pitted; relatively smooth; 5–7 nerved (the median present but inconspicuous). Upper glume 3 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; epaleate; sterile. The proximal lemmas awnless; thinly 2 nerved; more or less equalling the female-fertile lemmas to decidedly exceeding the female-fertile lemmas; similar in texture to the female-fertile lemmas (hyaline); not becoming indurated.

Female-fertile florets 1. Lemmas less firm than the glumes (hyaline); not becoming indurated; incised; 2 lobed; deeply cleft; awned. Awns 1; median; from a sinus; geniculate; hairless to hairy (glabrescent); much longer than the body of the lemma (8–9 cm long); entered by one vein. Lemmas hairless; non-carinate; without a germination flap; 1 nerved. Palea absent. Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Anthers about 3 mm long (the filaments short); not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases; free. Style bases adjacent. Stigmas 2.

Fruit, embryo and seedling. Fruit not noticeably compressed. Hilum short. Embryo large.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (the costals much narrower); of similar wall thickness costally and intercostally (thin walled). Mid-intercostal long-cells rectangular and fusiform; having markedly sinuous walls and having straight or only gently undulating walls. Microhairs present; elongated; clearly two-celled; panicoid-type. Stomata common. Subsidiaries mostly high triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells fairly common; in cork/silica-cell pairs and not paired (paired and solitary); silicified and not silicified. Intercostal silica bodies tall-and-narrow. Costal short-cells conspicuously in long rows. Costal silica bodies present and well developed; saddle shaped and ‘panicoid-type’; dumb-bell shaped; not sharp-pointed.

Transverse section of leaf blade, physiology. C4; XyMS–. PCR sheath outlines uneven. PCR sheath extensions absent. Mesophyll with radiate chlorenchyma. Leaf blade adaxially flat. Midrib conspicuous; having a conventional arc of bundles (a large median, with three or four smaller bundles on either side); with colourless mesophyll adaxially. The lamina symmetrical on either side of the midrib. Bulliforms present in discrete, regular adaxial groups (in places, but the epidermis mainly bulliform); in simple fans (in places), or associated with colourless mesophyll cells to form deeply-penetrating fans (in places); associating with colourless mesophyll cells to form arches over small vascular bundles (there often being a colourless cell adjacent to the epidermis on either side of a small bundle). Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present (with the larger bundles); forming ‘figures’ (the larger bundles with I’s). Sclerenchyma all associated with vascular bundles.

Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Andropogoneae; Andropogoninae. Soreng et al. (2015): Panicoideae; Andropogonodae; Andropogoneae; Anthistiriinae. 1–2 species.

Distribution, phytogeography, ecology. Tropical Africa.

Glycophytic. On shallow sandy soils.

References, etc. Leaf anatomical: this project.

Illustrations. • P. gossweileri (as P. monostachya): Jacques-Félix, 1962


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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: 13th November 2017. delta-intkey.com/grass’.

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