Ctenium elegans Kunth

Extinction risk predictions for the world's flowering plants to support their conservation (2024). Bachman, S.P., Brown, M.J.M., Leão, T.C.C., Lughadha, E.N., Walker, B.E. https://nph.onlinelibrary.wiley.com/doi/full/10.1111/nph.19592

Conservation

Predicted extinction risk: not threatened. Confidence: confident

Longhi-Wagner, H.M. & Cope, T.A. 2014. The genus Ctenium (Poaceae: Chloridoideae: Chlorideae) in Africa. Kew Bulletin 69: 9541. DOI https://doi.org/10.1007/s12225-014-9541-x

Type

Type: “Crescit in Senegalia”, M. Gay s.n. (holotype P, isotype K).

Morphology General Habit

Caespitose perennial, occasionally short-lived or even annual, 5 60 – 150 (180) cm, with or without a short non-scaly rhizome

Morphology Leaves

Leaf sheaths densely scabrid, with, or occasionally without, a tuft of hairs at the apex, the hairs 2.5 – 3 mm, not becoming fibrous with age; ligule 0.2 – 0.4 mm, truncate; leaf blades convolute to flat, 15 – 25 (35) cm × 2 – 3 mm, densely scabrid on both surfaces, occasionally with sparse hairs on the lower 1/5 of the adaxial surface, the hairs 2 – 3 mm

Morphology Reproductive morphology Inflorescences

Spike 1, (6) 9 – 26 (29) × 0.4 – 0.8 (1) cm; peduncle puberulous, without a ring of long spreading hairs at the base of the spike, rarely bearded with hairs 0.4 – 0.7 mm; rachis glabrous to slightly scabrid, shortly ciliate on the margins, the cilia 0.2 – 0.4 mm

Morphology Reproductive morphology Inflorescences Spikelets

Spikelets with 4 florets

Morphology Reproductive morphology Inflorescences Bracts Glume

Lower glume 2 – 3 mm, aristulate, 1-nerved, scabrid on the nerve, with or without sparse papillae Upper glume (4) 5 – 8 (9) mm, acuminate to aristulate, 2-nerved, slightly scabrid all over, shortly hirsute with hairs c. 0.2 mm and papillose on the lateral nerve; dorsal awn rudimentary to well-developed, sometimes varying in the same plant, (0.2) 1 – 3 (4) mm, slightly swollen at the base

Morphology Reproductive morphology Flowers Florets

Third floret well-developed; lemma 2.6 – 3 × 0.4 – 0.5 mm, lanceolate, glabrous on the back, sparsely ciliate on the middle of the margins, the cilia 0.3 – 0.4 mm, with (1) 3 – 5 bristles near the apex, these (1.2) 1.5 – 3 mm; awn subapical, 4 – 6 (10) mm; palea (1.8) 2.2 – 3 × 0.3 – 0.4 mm, generally with yellow papillae on the nerves Fourth floret poorly developed, reduced to a lemma 0.3 – 0.7 × 0.08 – 0.1 mm First floret barren, reduced to the lemma, 1.2 – 2 × 0.2 – 0.3 mm, narrowly linear, shortly bilobed, sparsely to subdensely pilose on the back, the hairs 0.3 – 0.4 mm, ciliate on the margins, the cilia 0.3 – 0.7 mm, with yellow papillae on the lateral nerves; awn (4.3) 5 – 12 (15) mm, inserted 0.5 – 0.7 mm from the tip Second floret reduced to the lemma or with a single stamen; lemma (1.5) 1.8 – 2 (2.5) × 0.2 – 0.3 mm, narrowly linear, obtuse, pilose on the back, the hairs 0.3 – 0.4 mm, ciliate on the margins, the cilia 0.3 mm below and 0.5 – 0.7 mm above, with yellow papillae on the lateral nerves and with (1) 4 – 5 (8) bristles near the apex, these (1) 2 – 3 mm; awn (4.5) 6 – 14 mm, inserted 0.5 mm from the tip; anther 2 – 2.5 mm

Morphology Reproductive morphology Fruits

Caryopsis 2 × 0.5 mm; hilum linear, c. \( \frac{2}{3} \) the length of the fruit

Distribution

Common in tropical West Africa; less common in tropical Northeast Africa.

Ecology

Ctenium elegans occurs at low altitudes up to 500 m, on sandy soils in disturbed areas around villages or in depleted tree savannas. It also occurs in sandy open grasslands and as a roadside weed.

Note

Ctenium elegans always has only 1 spike per flowering culm but there is great variation in its length (Fig. 5A, B). The most outstanding characteristic of the species, which differentiates it from others, is the constant presence of 1.5 – 3 mm bristles near the apex of the second and third lemmas (Fig. 5H, J). The presence of yellow glandular papillae on the lateral nerves of the first and second lemmas (Fig. 5G, H) and on the keel of the third palea (Fig. 5L) is also exclusive to this species, but very rarely these papillae are absent. This was found only in specimen Bral 16, but the bristles were present. Another exclusive feature of C. elegans is the variable length of the upper glume’s dorsal awn in some specimens, ranging from rudimentary to as much as 4 mm (Fig. 5C – E, K). The upper glume has both hairs and papillae on the lateral nerve (Fig. 5K), and thus differs from other African species in which the papillae are similar but the hairs, when present, are on the central nerve, below the awn. This is an interesting feature because it allows identification of the species simply by looking at the spike, avoiding unnecessary damage to the spikelet during dissection. When this feature is combined with the presence of a rudimentary awn on the upper glume, the identification of the species is even easier. The presence of aromatic leaves is reported on some herbarium labels.