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The grass genera of the world

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

Dilophotriche Jacq.-Fél.

~ Loudetiopsis p.p.

Habit, vegetative morphology. Annual, or perennial (culms erect, rather slender); caespitose. Culms 100–120 cm high; herbaceous; cylindrical; unbranched above; 4–6 noded. Culm nodes exposed; glabrous. Culm leaves present. Culm internodes hollow. Leaves not basally aggregated; non-auriculate. Leaf blades linear; narrow; often becoming involute setaceous, or not setaceous; flat, or rolled (becoming involute); without cross venation. Ligule a fringe of hairs. Contra-ligule absent.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.

Inflorescence. Inflorescence few spikeleted to many spikeleted; paniculate (diffuse, the branches often setulose); open; with capillary branchlets (often), or without capillary branchlets (but then the branchlets slender); espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets in triplets, or paired (rarely); not secund; pedicellate; not in distinct ‘long-and-short’ combinations (but the pedicels varying in length).

Female-fertile spikelets. Spikelets 7–12 mm long; compressed laterally; disarticulating above the glumes; disarticulating between the florets (above the L1 only in D. pobeguinii, above the L1 and above G2 in D. occidentalis). The upper floret conspicuously stipitate. Rachilla terminated by a female-fertile floret. Hairy callus present. Callus long (with long hairs); blunt (at the tip).

Glumes two; very unequal; (the upper) long relative to the adjacent lemmas; hairy (with long tubercle-based hairs), or hairless (glabrous); pointed; awnless; non-carinate; very dissimilar to similar (more or less lanceolate, the lower shorter and sometimes hairier with more prominent nerves). Lower glume shorter than the lowest lemma; convex on the back to flattened on the back; in D. pobeguinii tuberculate; 3 nerved. 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; paleate. Palea of the proximal incomplete florets fully developed (two keeled). The proximal incomplete florets male. The proximal lemmas lanceolate; awnless; 3 nerved; decidedly exceeding the female-fertile lemmas; less firm than the female-fertile lemmas (herbaceous-membranous); not becoming indurated.

Female-fertile florets 1. Lemmas decidedly firmer than the glumes; not becoming indurated (becoming leathery); incised; 2 lobed (the lobes finally setaceous); deeply cleft; awned. Awns 1, or 3; median, or median and lateral (if the lobes are considered awn-tipped); the median different in form from the laterals (if laterals are considered present); from a sinus; geniculate; hairless, or hairy; much longer than the body of the lemma; entered by several veins; deciduous (seemingly, in D. pobeguinii). The lateral awns (if considered as such) shorter than the median. Awn bases twisted; flattened. Lemmas hairy. The hairs in tufts, or not in tufts; in transverse rows (the lemma variously pilose, tufted on either side in the middle or with an fringe of long hairs on either side beneath the sinus). Lemmas non-carinate; 7 nerved; with the nerves confluent towards the tip. Palea present; relatively long; entire; awnless, without apical setae; textured like the lemma; 2-nerved; 2-keeled (the keels fairly thick and hard). Palea back glabrous. Palea keels wingless; glabrous. Lodicules present; 2; free; fleshy; glabrous; not toothed; not or scarcely vascularized. Stamens 3. Ovary apically glabrous. Styles free to their bases; free. Style bases widely separated. Stigmas 2; white, or brown.

Fruit, embryo and seedling. Fruit free from both lemma and palea; small; longitudinally grooved. Hilum long-linear. 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 somewhat fusiform, or rectangular; having markedly sinuous walls (the sinuosity fairly coarse). Microhairs present; elongated; clearly two-celled; panicoid-type. Stomata common. Subsidiaries non-papillate; dome-shaped (D. occidentalis), or triangular (with sharp points, in D. pobeguinii). Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common (abundant); mostly in cork/silica-cell pairs; silicified. Intercostal silica bodies irregularly cross-shaped (mostly more or less distorted, in D. pobeguinii). No microhairs or prickles seen in D. pobeguinii. Costal short-cells conspicuously in long rows. Costal silica bodies present and well developed; ‘panicoid-type’; long and short dumb-bell shaped (mostly with rather rough outlines, in D. pobeguinii).

Transverse section of leaf blade, physiology. C4; XyMS+ (? - see Jacques-Félix 1962), or XyMS– (indisputably, in D. pobeguinii). PCR sheath outlines uneven. PCR sheath extensions absent. Mesophyll without ‘circular cells’; traversed by columns of colourless mesophyll cells, or not traversed by colourless columns. Leaf blade adaxially flat. Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups, or not present in discrete, regular adaxial groups (the epidermis extensively bulliform, the groups mostly irregular); associating with colourless mesophyll cells to form arches over small vascular bundles. Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present (D. occidentalis), or absent (the abaxial fibres in D. pobeguinii as strands only); in D. occidentalis forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Arundinelleae. Soreng et al. (2015): Panicoideae; Tristachyideae. 3 species.

Distribution, phytogeography, ecology. West Africa.

Mesophytic. In damp pockets on rock outcrops.

References, etc. Morphological/taxonomic: Jacques-Félix 1962. Leaf anatomical: drawing of D. occidentalis, D. purpurea and D. tristachya in Jacques-Félix 1962; D. pobeguinii and D. occidentalis studied by us.

Illustrations. • Inflorescence detail (D. poeguinii). Dilophotriche pobeguinii, triplet of spikelets. • D. pobeguinii, female-fertile lemma: 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: 11th December 2017.’.