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The grass genera of the world

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

Heterachne Benth.

From the Greek heteros (different) and achne (chaff or scale), referring to different proximal (female-fertile) and distal (sterile) lemmas.

Type species: Type: H. gulliveri Benth.

Habit, vegetative morphology. Annual; caespitose. Culms 10–50 cm high; herbaceous; unbranched above. Culm nodes glabrous. Culm internodes hollow. Young shoots intravaginal. Leaves not basally aggregated; non-auriculate (but sometimes hairy at the auricle position). Leaf blades narrow; setaceous, or not setaceous; rolled (when dry); without abaxial multicellular glands; without cross venation; persistent. Ligule a fringed membrane (very reduced), or a fringe of hairs. Contra-ligule absent.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant, or all alike in sexuality; hermaphrodite, or hermaphrodite and sterile (there being abortive spikelets in all the clusters, and a lowermost cluster of imperfect spikelets, in the material examined of H. abortiva). Plants exposed-cleistogamous, or chasmogamous.

Inflorescence. Inflorescence a false spike, with spikelets on contracted axes (several globular heads in an interrupted spike), or paniculate (with sessile heads of spikelets in the upper leaf sheaths), or of spicate main branches; contracted; espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes very much reduced (to globular heads); persistent. Spikelets unaccompanied by bractiform involucres, not associated with setiform vestigial branches; solitary, or paired; not secund.

Female-fertile spikelets. Spikelets about 3–4 mm long; suborbicular to oblong; very much compressed laterally; disarticulating above the glumes (these deciduous); not disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret (and the prolongation sharply bent); hairless; the rachilla extension with incomplete florets. Hairy callus absent. Callus absent.

Glumes two; relatively large; very unequal to more or less equal; shorter than the spikelets; shorter than the adjacent lemmas; hairless; glabrous; pointed; awnless; carinate; similar (very compressed-complicate). Lower glume 1 nerved. Upper glume 1–3 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets 1–4 (in a fan-shaped cluster); merely underdeveloped.

Female-fertile florets 1(–3). Lemmas similar in texture to the glumes (membranous); becoming indurated (near the keel), or not becoming indurated; entire; blunt; awnless; hairless; glabrous; carinate. The keel winged. Lemmas without a germination flap; 1–3 nerved. Palea present; relatively long; entire; awnless, without apical setae; 2-nerved; 2-keeled. Palea keels winged (the wings broad, ciliate). Lodicules present; 2; fleshy; glabrous; not or scarcely vascularized. Stamens 3. Anthers minute; not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases (short). Stigmas 2.

Fruit, embryo and seedling. Fruit free from both lemma and palea (but enclosed); small; ellipsoid; compressed laterally. Hilum short. Pericarp fused. Embryo large; not waisted. Endosperm containing compound starch grains. Embryo with an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins meeting.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous (or the zonation fairly obscure, in H. abortiva). Papillae absent. Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally (fairly thick walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; elongated; clearly two-celled; panicoid-type. Microhair apical cell wall thinner than that of the basal cell and often collapsed. Microhairs 54–63 microns long. Microhair basal cells 24 microns long. Microhairs 9–12.5 microns wide at the septum. Microhair total length/width at septum 4.5–6.3. Microhair apical cells (25.5–)29.4–30 microns long. Microhair apical cell/total length ratio 0.47–0.54. Stomata common; 30–33 microns long. Subsidiaries predominantly triangular (in H. abortiva). Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common (e.g. in H. abortiva), or absent or very rare; in cork/silica-cell pairs to not paired; silicified. Intercostal silica bodies absent, or imperfectly developed; tall-and-narrow to crescentic (in H.abortiva). Costal short-cells predominantly paired. Costal silica bodies present throughout the costal zones; rounded (a few), or saddle shaped, or tall-and-narrow, or crescentic.

Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.

C4; XyMS+. PCR sheath outlines uneven. PCR sheaths of the primary vascular bundles interrupted; interrupted abaxially only. PCR sheath extensions present. Maximum number of extension cells 3–5. Leaf blade with distinct, prominent adaxial ribs; with the ribs more or less constant in size. Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups; in simple fans (their large median cells deeply penetrating), or associated with colourless mesophyll cells to form deeply-penetrating fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’. Sclerenchyma all associated with vascular bundles. The lamina margins with fibres.

Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Eragrostideae; Eragrostidinae. 3 species.

Distribution, phytogeography, ecology. Northern Australia.

Mesophytic. In damp depressions.

References, etc. Morphological/taxonomic: Hubbard 1935. Leaf anatomical: studied by us - H. abortiva (R. Br.) Druce.

Illustrations. • H. gulliveri: Hook. Ic. Pl. 13 (1877–79). • H. gulliveri: E. Hickman. • Inflorescence detail (H. gulliveri). • Close-up of inflorescence component (H. gulliveri). • Spikelet of H. gulliveri

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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.’.