| # The grass genera of the world |

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

### Thaumastochloa C.E. Hubb.

From the Greek haumastov (wonderful) and chloa (grass).

Habit, vegetative morphology. Annual, or perennial. Culms herbaceous. Culm nodes hairy, or glabrous. Culm internodes solid. The shoots not aromatic. Leaves non-auriculate. Leaf blades narrow; flat, or rolled (convolute); without cross venation; persistent. Ligule a fringed membrane to a fringe of hairs.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; hermaphrodite and sterile; overtly heteromorphic (the pedicelled spikelets greatly reduced).

Inflorescence. Inflorescence usually compound, of single, pedunculate, cylindrical, dorsiventral racemes. Rachides hollowed. Inflorescence spatheate, or espatheate (depending on interpretation); a complex of ‘partial inflorescences’ and intervening foliar organs, or not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes very much reduced, or spikelike (peduncled, slender, with one or few spikelets); solitary; with substantial rachides (hollowed); disarticulating; disarticulating at the joints (the rachis fragile, but the lowest spikelet falling with the peduncle, which becomes stiff, curved and pointed to function in dispersal), or falling entire (the only spikelet falling with the specialised peduncle). ‘Articles’ non-linear (concavo-convex, compressed or subterete); with a basal callus-knob; disarticulating transversely to disarticulating obliquely. Spikelets unaccompanied by bractiform involucres, not associated with setiform vestigial branches; paired (if the very reduced ‘pedicelled spikelet’ is interpreted as such); secund (the sessile spikelets in two alternating rows, on one side of the rachis); sessile and pedicellate (the pedicelled member vestigial); consistently in ‘long-and-short’ combinations; in pedicellate/sessile combinations. Pedicels of the ‘pedicellate’ spikelets discernible, but fused with the rachis. The ‘shorter’ spikelets hermaphrodite. The ‘longer’ spikelets sterile (and vestigial).

Female-sterile spikelets. The pedicelled spikelet reduced to a glume, or represented only by its fused pedicel.

Female-fertile spikelets. Spikelets compressed dorsiventrally; falling with the glumes (and with the joint). Rachilla terminated by a female-fertile floret. Hairy callus absent.

Glumes two; relatively large; more or less equal; long relative to the adjacent lemmas; awnless; very dissimilar (the lower indurated and sometimes rugulose, the upper hyaline and cymbiform). Lower glume two-keeled (wingless); convex on the back to concave on the back; not pitted; transversely rugose, or relatively smooth; 5–9 nerved. Upper glume 3–5 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; epaleate; sterile. The proximal lemmas awnless; 2 nerved (towards the margins); more or less equalling the female-fertile lemmas to decidedly exceeding the female-fertile lemmas; similar in texture to the female-fertile lemmas to decidedly firmer than the female-fertile lemmas (hyaline).

Female-fertile florets 1. Lemmas less firm than the glumes (hyaline); not becoming indurated; entire; blunt; awnless; hairless; non-carinate; 0–3 nerved. Palea present; 1-nerved, or 2-nerved, or nerveless. Lodicules present; 2; fleshy. Stamens 3. Anthers not penicillate. Ovary apically glabrous. Styles free to their bases.

Fruit, embryo and seedling. Fruit compressed dorsiventrally. Hilum short. Embryo large. Endosperm containing only simple starch grains. Embryo without an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins overlapping.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally (but the costals much smaller); of similar wall thickness costally and intercostally. Intercostal zones with typical long-cells (with a few short ones). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type; 45–51 microns long; 4.5–7.5 microns wide at the septum. Microhair total length/width at septum 6–11.3. Microhair apical cells 25–33 microns long. Microhair apical cell/total length ratio 0.57–0.65. Stomata common; 37–42 microns long. Subsidiaries triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells absent or very rare. Cushion-based macro-hairs present, prickle bases numerous. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’; not sharp-pointed.

Transverse section of leaf blade, physiology. C4; XyMS–. Mesophyll with radiate chlorenchyma. Leaf blade adaxially flat. Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups (in places, but the epidermis mostly irregularly bulliform); occasionally in simple fans (these large-celled, Zea-type). Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present; nowhere forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Special diagnostic feature. Spikelets not arranged as in Manisuris (q.v.).

Classification. Watson & Dallwitz (1994): Panicoideae; Andropogonodae; Andropogoneae; Rottboelliinae. Soreng et al. (2015): Panicoideae; Andropogonodae; Andropogoneae; Rottboelliinae. 7 species.

Distribution, phytogeography, ecology. Northeast India, Southeast Asia to Formosa, Philippines, Marianne & Caroline Is., Moluccas, Australia.

Woodland.

References, etc. Morphological/taxonomic: Hubbard 1936. Leaf anatomical: studied by us - Thaumastochloa ‘sp.’.

Illustrations. • General aspect (Thaumastochloa major): E. Hickman.

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: 15th June 2025. delta-intkey.com’.

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