The grass genera of the world
~ Loudetia Section Pseudotristachya C.E. Hubb., cf. Jacques-Felix 1962
Excluding Diandrostachya, Dilophotriche
Habit, vegetative morphology. Usually perennial. Culms 30–120 cm high; herbaceous (usually erect); sparsely branched above, or unbranched above. The branching simple. Culm nodes hairy (L. kerstingii), or glabrous. Culm internodes hollow. Plants unarmed. Leaves not basally aggregated; non-auriculate. Leaf blades linear, or lanceolate (L. tristachyoides); narrow (rigid); 2–7 mm wide; flat, or rolled (convolute); without cross venation; persistent. Ligule a fringe of hairs (and the blade pilose immediately above it); 0.3–0.5 mm long. Contra-ligule absent.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence paniculate; usually open, or contracted (rarely, but not spiciform); with capillary branchlets, or without capillary branchlets; espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets in triplets; not secund; pedicellate (the pedicels of all three spikelets short, arising together at the tip of the peduncle, which is often hooked); not in distinct long-and-short combinations (but the pedicels somewhat unequal).
Female-fertile spikelets. Spikelets 8–20 mm long; brown; compressed laterally, or not noticeably compressed; disarticulating above the glumes; disarticulating between the florets (more readily than between G2 and L1, cf. Loudetia); with conventional internode spacings. Rachilla terminated by a female-fertile floret. Hairy callus present. Callus short; blunt (truncate or slightly bifid).
Glumes two; very unequal; (the longer) long relative to the adjacent lemmas; hairy (usually with tubercle-based hairs); without conspicuous tufts or rows of hairs; pointed, or not pointed; awnless; very dissimilar (the G1 shorter, wider and hairier). Lower glume shorter than the lowest lemma; 3 nerved, or 5 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, membranous). The proximal incomplete florets male. The proximal lemmas awnless; 3 nerved; decidedly exceeding the female-fertile lemmas; similar in texture to the female-fertile lemmas; not becoming indurated.
Female-fertile florets 1. Lemmas similar in texture to the glumes to decidedly firmer than the glumes (leathery); not becoming indurated; incised (apically); 2 lobed; not deeply cleft; awned. Awns 1; median; from a sinus; geniculate; hairless (scabrous), or hairy (with short, appressed hairs); much longer than the body of the lemma; entered by one vein. Lemmas hairy, or hairless; non-carinate (dorsally rounded); without a germination flap; 5–9 nerved. Palea present; relatively long (linear); apically notched; awnless, without apical setae; thinner than the lemma; not indurated (membranous to leathery); 2-nerved; 2-keeled (the keels leathery). Palea keels wingless; glabrous. Lodicules present; 2; free; fleshy; not or scarcely vascularized. Stamens 2. Anthers 2.5 mm long; not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases. Stigmas 2; red pigmented (purple).
Fruit, embryo and seedling. Fruit longitudinally grooved, or not 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 (in L. chrysothrix, the costals narrower); of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; more or less spherical; panicoid-type; 66–75 microns long; 6.6–8.4 microns wide at the septum. Microhair total length/width at septum 7.9–11.3. Microhair apical cells 28–33 microns long. Microhair apical cell/total length ratio 0.42–0.46. Stomata common; 30–40.5 microns long. Subsidiaries low dome-shaped (consistently, in L. chrysothrix). Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; not paired (but often adjoining small prickles, in L. chrysothrix). Costal short-cells conspicuously in long rows. Costal silica bodies panicoid-type; dumb-bell shaped (but in the material of L. chrysothrix seen, these all seem to lack the isthmus, so that the actual silica takes the form of more or less round, saddle-shaped or crescentic pieces, occurring two per cell); not sharp-pointed.
Transverse section of leaf blade, physiology. C4; XyMS+ (e.g. L. chrysothrix), or XyMS (e.g. L. ambiens). PCR sheath outlines uneven. PCR sheath extensions present. Maximum number of extension cells 3. PCR cell chloroplasts centrifugal/peripheral. Mesophyll in places traversed by columns of colourless mesophyll cells. Leaf blade with distinct, prominent adaxial ribs; with the ribs very irregular in sizes. Midrib not readily distinguishable; with one bundle only, or having a conventional arc of bundles (the large bundle accompanied on either side by a minor one). Bulliforms present in discrete, regular adaxial groups (in each furrow); associated with colourless mesophyll cells to form deeply-penetrating fans (commonly linked with traversing columns of colourless cells); associating with colourless mesophyll cells to form arches over small vascular bundles. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with all the major bundles - the minor ones with only abaxial girders, or with strands only); forming figures. Sclerenchyma all associated with vascular bundles.
Special diagnostic feature. The lower glume shorter than the female-fertile lemma.
Cytology. Chromosome base number, x = 10. 2n = 20.
Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Arundinelleae. Soreng et al. (2015): Panicoideae; Tristachyideae. 11 species.
Distribution, phytogeography, ecology. West Africa.
Helophytic (sometimes), or mesophytic; species of open habitats; glycophytic. Savanna, usually in woodland or shallow pockets on bare rocks, rarely in swamps.
References, etc. Leaf anatomical: Metcalfe 1960; studied by us - L. chrysothrix (Nees) Conert.
Illustrations. • L. ambiens: Jacques-Félix, 1962. • L. chrysothrix, as Tristachya: Kunth (1835)
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. delta-intkey.com/grass’.