The grass genera of the world
Habit, vegetative morphology. Annual. Culms 30–60 cm high; herbaceous; unbranched above. Culm nodes glabrous. Plants unarmed. Leaves not basally aggregated. Leaf blades narrow; 2–4 mm wide (about 4 cm long); exhibiting multicellular glands abaxially. The abaxial leaf blade glands on the blade margins. Leaf blades without cross venation; persistent. Ligule present; very short, lacerate or a line of hairs, in different descriptions.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence of spicate main branches (of slender racemes from the main rachis); non-digitate. Primary inflorescence branches 12–25 (about 6 cm long, with few spikelets). Inflorescence espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary.
Female-fertile spikelets. Spikelets 5–6 mm long; not noticeably compressed (terete); disarticulating above the glumes; disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret. Hairy callus present.
Glumes two; very unequal to more or less equal; exceeding the spikelets (enfolding the florets); long relative to the adjacent lemmas; hairless (glabrous, with scabridulous keels); pointed (acute or acuminate); awnless; similar (narrowly lanceolate, membranous). Lower glume much exceeding the lowest lemma; 1 nerved. Upper glume 1 nerved. Spikelets with female-fertile florets only, or with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets 1; merely underdeveloped (vestigial). Spikelets without proximal incomplete florets.
Female-fertile florets 2. Lemmas not becoming indurated; incised; 2 lobed; not deeply cleft (bidentate); shortly awned. Awns 1; median; from a sinus; non-geniculate; hairless; much shorter than the body of the lemma (about 1 mm long). Lemmas hairy (villous on the lateral nerves, the nerves grey-green); non-carinate; 3 nerved. Palea present; relatively long; entire to apically notched (emarginate); awnless, without apical setae; not indurated; 2-nerved; 2-keeled. Palea keels hairy (conspicuously fringed, the hairs grey-green). Lodicules minute or missing. Stamens 3. Anthers 0.4–0.5 mm long. Ovary apically glabrous. Stigmas 2.
Fruit, embryo and seedling. Fruit ellipsoid; slightly compressed dorsiventrally.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (the costals narrower and longer); of similar wall thickness costally and intercostally (walls of medium thickness). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; elongated; clearly two-celled; chloridoid-type (the basal cell quite long and expanding distally). Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhairs (27–)28.5–33(–36) microns long. Microhair basal cells 21–24 microns long. Microhairs 6.9–8.4 microns wide at the septum. Microhair total length/width at septum 3.2–4.8. Microhair apical cells 7.5–9 microns long. Microhair apical cell/total length ratio 0.23–0.33. Stomata common; 19.5–24–27 microns long. Subsidiaries all dome-shaped. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs and not paired (some solitary); silicified. Intercostal silica bodies present and perfectly developed; mostly saddle shaped (small). Costal short-cells conspicuously in long rows. Costal silica bodies present in alternate cell files of the costal zones; exclusively saddle shaped; not sharp-pointed.
Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.
C4; XyMS+. PCR sheaths of the primary vascular bundles interrupted; interrupted abaxially only. PCR sheath extensions absent. Leaf blade adaxially flat. Midrib conspicuous (via a larger bundle with more abaxial sclerenchyma, and a small sharp keel); with one bundle only. Bulliforms present in discrete, regular adaxial groups; in simple fans (the large median cell deeply penetrating). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (but few: most bundles with a broad abaxial girder and a small adaxial strand); forming figures (a few primaries with Is). Sclerenchyma all associated with vascular bundles. The lamina margins with fibres.
Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage (cf. Leptochloa). Soreng et al. (2015): Chloridoideae; Cynodonteae. 1 species (P. biflora).
Distribution, phytogeography, ecology. Tropical East Africa.
References, etc. Morphological/taxonomic: Napper 1963. Leaf anatomical: studied by us.
Special comments. Fruit data wanting. Illustrations. • P. biflora, abaxial epidermis of leaf blade: 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. delta-intkey.com/grass’.