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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 (P. gossweileri).

Distribution, phytogeography, ecology. Tropical Africa.

Glycophytic. On shallow sandy soils.

References, etc. Leaf anatomical: studied by us - P. gossweileri Stapf.

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

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: 11th December 2017.’.