The grass genera of the world
Habit, vegetative morphology. Perennial; stoloniferous and decumbent. Culms about 10–40 cm high; herbaceous; unbranched above; 3 noded. Culm nodes exposed; glabrous. Culm leaves present. Culm internodes solid. Leaves not basally aggregated; non-auriculate. The sheaths keeled. Leaf blades linear; narrow; 4–6 mm wide; folded; without abaxial multicellular glands; pseudopetiolate; without cross venation; disarticulating from the sheaths, or persistent (?). Ligule a fringe of hairs. Contra-ligule absent.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets all alike in sexuality; hermaphrodite.
Inflorescence. Inflorescence a single spike, or of spicate main branches; digitate to non-digitate. Primary inflorescence branches 1–2(–4). Inflorescence espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary; secund (on one side of the rachis); biseriate; imbricate.
Female-fertile spikelets. Spikelets about 3 mm long; detectably adaxial (but twisted to lie flatwise, cf. Chloris); compressed laterally; disarticulating above the glumes; not disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret; hairless; the rachilla extension with incomplete florets. Hairy callus present. The callus hairs white (short). Callus pointed.
Glumes two; more or less equal; shorter than the spikelets; shorter than the adjacent lemmas; hairless; scabrous (along the midvein); pointed; awnless (but the lower conspicuously mucronate); carinate; very dissimilar (the lower much larger). Lower glume 1 nerved. Upper glume 1 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets 1; red, male or sterile; awned.
Female-fertile florets 1. Lemmas becoming broadly winged above, the wings membranous, bilobed, spreading out at maturity; similar in texture to the glumes; incised; 2 lobed; not deeply cleft; awned. Awns 1; median; from a sinus to dorsal (from between the lobes, or just behind them); from near the top; non-geniculate (slender); flexuous; hairless; much longer than the body of the lemma; entered by one vein; persistent. Awn bases not twisted; not flattened. Lemmas hairless; glabrous, or scabrous (along the margins); carinate; without a germination flap; 3 nerved (below), or 5–7 nerved (above, the laterals branching into the wings); with the nerves non-confluent. Palea present; relatively long; entire; awnless, without apical setae; textured like the lemma; not indurated; 2-nerved; 2-keeled. Palea back glabrous. Palea keels winged; hairy. Lodicules absent. Stamens 3. Anthers about 1 mm long; not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases; free. Style bases widely separated. Stigmas 2; red pigmented.
Fruit, embryo and seedling. Fruit ellipsoid; compressed dorsiventrally, or trigonous; glabrous; smooth. Hilum short. Pericarp thin; loosely adherent. Embryo large; not waisted. Endosperm hard.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally. Intercostal zones with typical long-cells. Mid-intercostal long-cells rectangular; having markedly sinuous walls (coarsely so). Microhairs present; more or less spherical; clearly two-celled; chloridoid-type. Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhair basal cells 9 microns long. Microhair total length/width at septum about 1.4. Microhair apical cell/total length ratio about 0.6. Stomata common. Subsidiaries non-papillate; triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs; silicified and not silicified. Intercostal silica bodies imperfectly developed; rounded, crescentic, tall-and-narrow, cross-shaped, and oryzoid-type. Costal short-cells conspicuously in long rows (but the short-cells mostly quite long), or neither distinctly grouped into long rows nor predominantly paired (in places). Costal silica bodies present and well developed; present in alternate cell files of the costal zones; saddle shaped.
Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.
C4; XyMS+. PCR sheath outlines even. PCR sheaths of the primary vascular bundles interrupted; interrupted both abaxially and adaxially. PCR sheath extensions absent. Mesophyll not Isachne-type. Leaf blade nodular in section; with the ribs more or less constant in size. Midrib conspicuous; with one bundle only; with colourless mesophyll adaxially (some colourless tissue adjacent to a large median bulliform group). The lamina symmetrical on either side of the midrib. Bulliforms present in discrete, regular adaxial groups (in places), or not present in discrete, regular adaxial groups (in places constituting most of the epidermis); commonly in simple fans. All the vascular bundles accompanied by sclerenchyma (but the smallest usually with only one or two fibres abaxially). Combined sclerenchyma girders present; forming figures (the lateral primaries with Is). Sclerenchyma all associated with vascular bundles. The lamina margins with fibres.
Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae (as a synonym?); Cynodonteae; Eleusininae. 1 species.
Distribution, phytogeography, ecology. Madagascar.
References, etc. Morphological/taxonomic: Camus 1957. Leaf anatomical: this project.
Illustrations. • P. humbertiana (as Chloris): Anderson, Brig. Young Univ. Sci. Bull. (1974). • Inflorescence detail of P. humbertiana: this project. • Inflorescence close-up of P. humbertiana: this project. • Dissected out spikelet of P. humbertiana: this project. Pterochloris humbertiana. Left to right: glumes, long-awned lemma and palea of hermaphrodite floret (separated), and (right) a long-awned distal incomplete floret. glumes. lemma (left) and plea (right) of hermaphrodite floret. distal incomplete floret
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: 13th November 2017. delta-intkey.com/grass’.