The grass genera of the world
Type species: Type: H. aquatica Lazarides.
Habit, vegetative morphology. Annual, or perennial (aquatic to hydrophytic); caespitose (H. cravenii, erect, not submerged, to 1 m high), or decumbent (H. aquatica, floating from submerged tufts). Culms 50–100 cm high; herbaceous; branched above (at least sometimes), or unbranched above (?). The branching simple, or fastigiate (in H. cravenii). Culm leaf sheaths rounded. Culm internodes hollow (and aerenchymatous). Leaves not basally aggregated; non-auriculate. Leaf blades narrow; without cross venation; persistent. Ligule a fringe of hairs.
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 on different branches of the same inflorescence (female spikelets in appressed spiciform racemes below, male spikelets on the main axis above). The spikelets overtly heteromorphic.
Inflorescence. Inflorescence of spicate main branches. Primary inflorescence branches borne biseriately on one side of the main axis. Inflorescence axes not ending in spikelets (the branch rachides and the panicle axis briefly bare-tipped). Rachides hollowed. Spikelets all partially embedded in the rachis (to some extent). Inflorescence espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary; secund; biseriate. Pedicel apices discoid.
Female-sterile spikelets. Male spikelets 3.5–5 mm long, with 2 florets, both staminate with three stamens or one neuter. The male spikelets with glumes; 2 floreted. The lemmas awnless. Male florets 1, or 2; 3 staminate.
Female-fertile spikelets. Spikelets 2–2.75 mm long; oblong, or elliptic, or obovate; abaxial; compressed dorsiventrally; falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus absent.
Glumes two; very unequal; shorter than the adjacent lemmas, or long relative to the adjacent lemmas; dorsiventral to the rachis; hairless; not pointed; awnless; non-carinate; very dissimilar (both membranous, the upper much larger and more substantial). Lower glume 0–3 nerved. Upper glume 5–7 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. The proximal incomplete florets 1; epaleate; sterile. The proximal lemmas awnless; 5–7 nerved; more or less equalling the female-fertile lemmas; less firm than the female-fertile lemmas (membranous); not becoming indurated.
Female-fertile florets 1. Lemmas decidedly firmer than the glumes (leathery to crustaceous); striate (or striolate); becoming indurated; yellow in fruit, or brown in fruit; entire; pointed; awnless (apiculate); hairless; non-carinate; having the margins lying flat on the palea; with a clear germination flap; 5 nerved. Palea present; relatively long; entire; awnless, without apical setae; textured like the lemma; indurated, or not indurated; 1-nerved; 2-keeled. Lodicules present; 2; free; fleshy; glabrous. Stamens 0. Ovary apically glabrous. Styles fused. Stigmas 2; red pigmented.
Fruit, embryo and seedling. Fruit small (1.5–1.75 mm long); compressed dorsiventrally. Hilum short. Embryo large.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally (long-rectangular); of similar wall thickness costally and intercostally (thin walled). Mid-intercostal long-cells having markedly sinuous walls. Microhairs present; panicoid-type (distal cells very flimsy and often missing); 34.5–36 microns long; 5.4–7.5 microns wide at the septum. Microhair total length/width at septum 4.8–6.7. Microhair apical cells 18–21 microns long. Microhair apical cell/total length ratio 0.52–0.58. Stomata common; 33–39 microns long. Subsidiaries triangular. Guard-cells overlapping to flush with the interstomatals (flush). Intercostal short-cells common; in cork/silica-cell pairs (mostly superposed); silicified, or not silicified. Costal short-cells conspicuously in long rows, or neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies panicoid-type; nodular.
Transverse section of leaf blade, physiology. C4; XyMS. PCR sheath outlines uneven. PCR sheath extensions absent. Leaf blade adaxially with numerous large, inflated hairs, clustered on the ribs and less frequent intercostally. Midrib not readily distinguishable; with one bundle only. Bulliforms not present in discrete, regular adaxial groups (the epidermis extensively bulliform). Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders absent (with the adaxial sclerenchyma confined to tiny strands, associated with the larger bundles). Sclerenchyma all associated with vascular bundles.
Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae. Soreng et al. (2015): Panicoideae; Panicodae; Paniceae; Cenchrinae. 2 species.
Distribution, phytogeography, ecology. North Australia.
Hydrophytic to helophytic.
References, etc. Morphological/taxonomic: Lazarides 1979. Leaf anatomical: studied by us - H. aquatica Lazarides, H. craveni Lazarides.
Illustrations. • H. aquatica, H. cravenii: Lazarides, 1979. • H. aquatica, abaxial epidermis of leaf blade: this project. • H. aquatica, abaxial epidermis of leaf blade: this project. • H. aquatica, Leaf blade T.S. with inflated macrohairs: original. Hygrochloa aquatica. Inflated adaxial macrohairs.
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’.