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The grass genera of the world

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

Ectrosia R.Br.

From the Greek ektrosis (miscarriage), referring to spikelets with only 1–2 proximal hermaphrodite flowers, with males or empty lemmas above them.

Type species: Type: E. leporina R.Br.

Excluding Ectrosiopsis, Planichloa

Habit, vegetative morphology. Annual, or perennial; caespitose. Culms 10–60 cm high; herbaceous; branched above, or unbranched above. The branching simple. Culm nodes glabrous. Culm internodes hollow. Leaves mostly basal, or not basally aggregated; non-auriculate. Leaf blades narrow; setaceous, or not setaceous; from setaceous in E. agrostoides to flat and up to 3 mm wide in E. leporina; without abaxial multicellular glands; without cross venation; persistent. Ligule a fringed membrane (very narrow), or a fringe of hairs. Contra-ligule absent.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets all alike in sexuality. Plants exposed-cleistogamous, or chasmogamous.

Inflorescence. Inflorescence paniculate (or almost reduced to a raceme of racemes); open to contracted; with capillary branchlets (E. eragrostoides), or without capillary branchlets; non-digitate. Inflorescence with axes ending in spikelets. Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets solitary; secund, or not secund; pedicellate.

Female-fertile spikelets. Spikelets 1.5–13 mm long; compressed laterally; disarticulating above the glumes; not disarticulating between the florets; with distinctly elongated rachilla internodes between the florets (the one above the glumes shorter than the rest). Rachilla prolonged beyond the uppermost female-fertile floret; hairless; the rachilla extension with incomplete florets. Hairy callus absent.

Glumes two; very unequal; shorter than the spikelets; shorter than the adjacent lemmas; hairless; glabrous; pointed, or not pointed; awnless; carinate; similar. Lower glume 1 nerved. Upper glume 1 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets clearly specialised and modified in form (long-awned, or reduced to awns). Spikelets without proximal incomplete florets.

Female-fertile florets 1–20. Lemmas similar in texture to the glumes (thinly membranous); not becoming indurated; entire, or incised; when entire pointed, or blunt; when incised, 2 lobed; not deeply cleft; awned. Awns 1; median; from a sinus, or apical; non-geniculate; hairless (scabrous); much shorter than the body of the lemma to much longer than the body of the lemma. Lemmas hairless; glabrous, or scabrous; carinate; without a germination flap; 1–9 nerved. Palea present; relatively long; entire; awnless, without apical setae; not indurated; 2-nerved; strongly 2-keeled. Palea keels wingless; hairy (ciliate). Lodicules present; 2; fleshy; glabrous; not or scarcely vascularized. Stamens 3. Anthers very short; not penicillate. Ovary apically glabrous. Styles free to their bases. Stigmas 2; white.

Fruit, embryo and seedling. Fruit small; ellipsoid; not noticeably compressed. Hilum short. Pericarp fused. Embryo large. Endosperm hard; 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. Papillae absent. 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 (45–)48–66(–69) microns long. Microhair basal cells 21 microns long. Microhairs (4.5–)5.4–6(–6.6) microns wide at the septum. Microhair total length/width at septum 7.5–11.1. Microhair apical cells (19.5–)25.5–36(–39) microns long. Microhair apical cell/total length ratio 0.43–0.64. Stomata common; 24–27 microns long. Subsidiaries low dome-shaped, or triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs (E. leporina), or not paired (solitary, in the other species seen); silicified (E. leporina, with cork/silica-cell pairs), or not silicified. Intercostal silica bodies present and perfectly developed; in E. leporina tall-and-narrow and oryzoid-type. Costal short-cells predominantly paired. Costal silica bodies present throughout the costal zones; crescentic (mostly), or saddle shaped (a few), or tall-and-narrow (a few).

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 both abaxially and adaxially. PCR sheath extensions present. Maximum number of extension cells 1–6. Mesophyll with radiate chlorenchyma. Leaf blade with distinct, prominent adaxial ribs to adaxially flat; 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 (the median cells large and deeply penetrating). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with all the primaries); forming ‘figures’ (anchors and I’s in the primaries). 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. 12 species.

Distribution, phytogeography, ecology. Tropical Australia.

Species of open habitats. Poor sandy soils.

References, etc. Leaf anatomical: this project.

Illustrations. • E. leporina: Kunth (1835). • E. schultzii: Gardner, 1952. • Inflorescence. • Inflorescence (part), E. schultzii. • Inflorescence (part), aff. E. scabrida. • Spikelets of E. schultzii. Ectrosia schultzii. Spikelets with terminal florets reduced to awns. • Spikelet with modified sterile florets. Ectrosia sp. Spikelet with sterile, modified terminal florets


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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: 13th November 2017. delta-intkey.com/grass’.

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