Potamophila R.Br.
From the Greek potamos (river) and -philus (loving), alluding to the habitat of the only species.
Habit, vegetative morphology. Perennial; rhizomatous and caespitose. The flowering culms leafy. Culms 30–150 cm high; herbaceous. Culm nodes glabrous. Culm internodes hollow. Young shoots extravaginal. Leaves not basally aggregated; auriculate, or non-auriculate; without auricular setae. Leaf blades linear; narrow; 4–6 mm wide; not pseudopetiolate; without cross venation; disarticulating from the sheaths, or persistent; rolled in bud; an unfringed membrane; not truncate (acute or lacerate); 4–15 mm long. Contra-ligule absent.
Reproductive organization. Plants bisexual, with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant (hermaphrodite and unisexual); hermaphrodite and female-only, or hermaphrodite and male-only; homomorphic.
Inflorescence. Inflorescence paniculate; open (to loosely contracted); with capillary branchlets; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelets not secund; pedicellate.
Female-fertile spikelets. Spikelets unconventional (by virtue of reduced glumes, cf. Oryza); 3–5.5 mm long; strongly compressed laterally; disarticulating above the glumes (i.e., above the tiny cupule representing them); with conventional internode spacings (i.e. the floret not stipitate). Rachilla terminated by a female-fertile floret. Hairy callus absent.
Glumes present to absent (vestigial); if considered present, two; minute (reduced to a cupular or bilobed rim); more or less equal; shorter than the adjacent lemmas; joined; awnless. Lower glume 0 nerved. Upper glume 0 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 2; epaleate; sterile. The proximal lemmas ovate; awnless; 0 nerved; exceeded by the female-fertile lemmas (very small, less than 1/8 to 1/4 the spikelet length); less firm than the female-fertile lemmas to similar in texture to the female-fertile lemmas (membranous); not becoming indurated.
Female-fertile florets 1. Lemmas membranous or thinly chartaceous; not becoming indurated; entire; pointed to blunt; awnless; hairless (often scaberulous on the sides); non-carinate (‘sub-keeled’); 5 nerved. Palea present; relatively long; not clasped by the lemma; entire; awnless, without apical setae; textured like the lemma; not indurated; several nerved (three nerved); one-keeled. Lodicules present; 2; free; membranous; glabrous. Stamens 6. Ovary glabrous. Styles free to their bases. Stigmas 2.
Fruit, embryo and seedling. Fruit compressed dorsiventrally to not noticeably compressed. Hilum long-linear. Embryo small; with an epiblast; without a scutellar tail; with a negligible mesocotyl internode. Embryonic leaf margins meeting.
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. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type; (34.5–)39–45(–51) microns long; 7.5–8.4–9 microns wide at the septum. Microhair total length/width at septum 4.3–6.1. Microhair apical cells (12–)16.5–21(–22.5) microns long. Microhair apical cell/total length ratio 0.35–0.47. Stomata common; 19.5–21 microns long. Subsidiaries dome-shaped (mostly), or dome-shaped. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs, or not paired; silicified, or not silicified. Costal short-cells predominantly paired, or neither distinctly grouped into long rows nor predominantly paired (rarely). Costal silica bodies oryzoid to ‘panicoid-type’ (mostly), or tall-and-narrow (a few); not sharp-pointed.
Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma; without adaxial palisade; with arm cells; with fusoids. The fusoids external to the PBS (short). Leaf blade with distinct, prominent adaxial ribs; with the ribs more or less constant in size, or with the ribs very irregular in sizes. Midrib conspicuous; having complex vascularization. Bulliforms present in discrete, regular adaxial groups; in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’. Sclerenchyma all associated with vascular bundles.
Taxonomy. Bambusoideae; Oryzodae; Oryzeae.
Distribution, ecology, phytogeography. 1 species; Australia. Helophytic; glycophytic.
Australian. North and East Australian. Temperate and South-Eastern Australian.
References, etc. Leaf anatomical: this project.
Illustrations. • Transverse secction of leaf blade. Potamophila parviflora.
Cite this publication as: Watson, L., and Dallwitz, M. J. (1992 onwards). ‘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.’ http://biodiversity.uno.edu/delta/. Version: 18th August 1999. Dallwitz (1980), Dallwitz, Paine and Zurcher (1993 onwards, 1998), and Watson and Dallwitz (1994), and Watson, Dallwitz, and Johnston (1986) should also be cited (see References).
