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The grass genera of the world

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

Phyllorhachis Trimen

Habit, vegetative morphology. Perennial (with slender culms); rhizomatous. Culms scrambling, 50–130 cm high (or more); herbaceous; to 0.2 cm in diameter; branched above. Culm nodes hairy, or glabrous. Culm leaf sheaths present; persistent (with the blades, above), or deciduous (from the bases of the old culms). Culm internodes hollow. Plants unarmed. Young shoots extravaginal. Leaves not basally aggregated; non-auriculate; without auricular setae. Leaf blades lanceolate to ovate-lanceolate; broad; 10–25 mm wide (and to 12 cm long); sagittate; flat; pseudopetiolate (the pseudopetiole to 2.5 mm long); without cross venation; disarticulating from the sheaths (in association with culm branching). Ligule a fringe of hairs; 0.2 mm long. Contra-ligule absent.

Reproductive organization. Plants monoecious with all the fertile spikelets unisexual; without hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; female-only and male-only. The male and female-fertile spikelets mixed in the inflorescence (single female spikelets basal to male spikelets in the very contracted branches - glomerules - of the terminal inflorescences, and with female spikelets in small, homogamous axillary inflorescences of 1 or 2 spikelets each). The spikelets overtly heteromorphic.

Inflorescence. Inflorescence terminal, consisting of heterogamous racemules each of 3–4 spikelets, borne on flattened secondary rachides arranged in two series on one side of an expanded, herbaceous, primary rachis; and sometimes also with axillary, homogamous racemules of 2–3 female spikelets on slender rachides. Inflorescence axes not ending in spikelets (with a scabrid bristle in each glomerule seeming to represent the branch tip). Rachides flattened and winged (spathe-like). Inflorescence espatheate (but the rachis flattened, spathe-like); not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes disarticulating; falling entire (i.e., the racemules fall from the persistent main axis). Spikelets consistently in ‘long-and-short’ combinations (in the terminal inflorescence). The ‘shorter’ spikelets female-only and male-only. The ‘longer’ spikelets male-only and sterile.

Female-sterile spikelets. Male spikelets with glumes 2, short, similar, keel-less, oblong or oval, awnless; G1 nerveless, G2 1-nerved; one proximal, 3-nerved sterile lemma; one oblong, 5–7 nerved fertile lemma enclosing a 2-nerved palea and 6 free stamens with 2.5 mm anthers. Rachilla of male spikelets terminated by a male floret. The male spikelets with glumes; with proximal incomplete florets; 2 floreted (the proximal sterile). Male florets 1; 6 staminate. The staminal filaments free.

Female-fertile spikelets. Spikelets unconventional (the ‘G1’ and palea highly peculiar); 10–16 mm long; ovate; abaxial (with respect to the main axis); compressed laterally, or not noticeably compressed, or compressed dorsiventrally (?); falling with the glumes (the glomerules disarticulating). Rachilla terminated by a female-fertile floret. Hairy callus absent. Callus absent.

Glumes two; more or less equal; shorter than the adjacent lemmas; awned (G1 awn-like); carinate (G2); very dissimilar (the G1 subulate, rigid and awnlike, the G2 oblong and firm). Lower glume 0–1 nerved. Upper glume 5–9 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. The proximal incomplete florets 1; sterile (reduced, rigid, thick). The proximal lemmas awnless; many nerved, broadly lanceolate, sulcate in the back; more or less equalling the female-fertile lemmas to decidedly exceeding the female-fertile lemmas; decidedly firmer than the female-fertile lemmas.

Female-fertile florets 1. Lemmas caudate-acuminate; not becoming indurated; entire; pointed; awnless; hairless; non-carinate; without a germination flap; 11–17 nerved. Palea present (sulcate between the two principal nerves); relatively long; entire (pointed); awnless, without apical setae; several nerved (8–12). Lodicules present; 2; free; membranous; glabrous. Stamens 0 (6 rudiments only). Ovary apically glabrous. Styles fused (into one, long). Stigmas 2; creamy white.

Fruit, embryo and seedling. Fruit free from both lemma and palea; medium sized (6–7 mm long); fusiform; slightly longitudinally grooved; not noticeably compressed. Hilum long-linear. Embryo small (about 1/6 the length of the fruit).

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Intercostal zones exhibiting many atypical long-cells (many being rather short). Mid-intercostal long-cells having markedly sinuous walls (thin walled). Microhairs present; panicoid-type; 42–50 microns long. Microhair apical cells 25–30 microns long. Microhair apical cell/total length ratio 0.6. Stomata common. Subsidiaries triangular. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Intercostal silica bodies tall-and-narrow, or tall-and-narrow and oryzoid-type. Macrohairs present. Costal short-cells conspicuously in long rows. Costal silica bodies oryzoid (mostly), or saddle shaped (tendency), or ‘panicoid-type’ (tendency); when panicoid type, tending to cross shaped; not sharp-pointed.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma; with arm cells; without fusoids. Leaf blade adaxially flat. Midrib conspicuous; having a conventional arc of bundles (a median bundle and 2 small laterals). Bulliforms present in discrete, regular adaxial groups; in simple fans (the groups wide). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Special diagnostic feature. Spikelets borne on one side of a broad, leaflike rachis.

Cytology. Chromosome base number, x = 12. 2n = 24. 2 ploid.

Classification. Watson & Dallwitz (1994): Bambusoideae; Oryzodae; Phyllorhachideae. Soreng et al. (2015): Oryzoideae; Phyllorachideae (or Oryzeae). 1 species (P. sagittata).

Distribution, phytogeography, ecology. Southern tropical Africa.

Mesophytic; shade species; glycophytic. In riverine forests.

References, etc. Leaf anatomical: Metcalfe 1960.

Illustrations. • P. sagittata: Jacques-Félix, 1962. • P. sagittata, leaf blade anatomy: 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.’.