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- Festuca fusca L., Syst. Nat., ed. 10, 2: 876. 1759. Leptochloa fusca (L.) Kunth, Révis. Gramin. 1: 91. 1829. Diplachne fusca (L.) P. Beauv. ex Stapf, Fl. Cap. 7: 591. 1900, nom. illeg. hom. Diplachne fusca (L.) P. Beauv. ex Stuck., Anales Mus. Nac. Buenos Aires 11: 128. 1904, nom. illeg. hom. Uralepis fusca (L.) Steud., Syn. Pl. Glumac. 1: 247. 1855.
Palestine, F Hasselquist s.n. (lectotype: LINN 92.21!; designated by Phillips, Fl. Trop. East Afr. Gram. (2): 281. 1974)
Annuals or perennials. Culms 3 cm long (when prostrate) to 170 cm tall, 1–8 mm wide at base, round or sometimes flattened, ascending to erect (sometimes completely prostrate at higher altitudes) or geniculate and rooting at lower nodes (facultatively stoloniferous), branched or unbranched; nodes glabrous; internodes (0.5–)3–26 cm long, soft or sometimes slightly lignified, hollow. Leaf sheaths longer or shorter than the internodes, round or flattened, glabrous on sides and margins; ligules (1.5–)5–12(–15) mm long, hyaline to membranous, apically attenuate but often becoming lacerated due to mechanical damage; blades (3–)5–50 ×0.2–0.6 cm, flat but becoming inrolled when dry, glabrous to somewhat scabrous above and below. Panicles (1.5–)15–105 ×2–30 cm, partially inserted below (subspp. muelleri and fascicularis or occasionally subsp. fusca) to completely exserted at maturity; with (3–)5–35 branches; the branches (1.5–)3–20 cm long, alternate along the rachis, sometimes reflexed or steeply erect but mostly somewhat ascending, stiff, minutely scabrous, axils glabrous. Spikelets 5–12(–14) mm long, shortly pedicillate, sometimes distant near base of branches but overlapping near branch tips; florets (4–)6–12(–20); callus glabrous or hairy; lower glumes 1.0–3.5 (–4.9) mm long, membranous, narrowly ovate to ovate, usually scabrous on the midnerve, apex broadly acute to acute, awnless or infrequently shortly awned; upper glumes 1.8–5.5 mm long, elliptic to usually ovate or widely ovate (or sometimes obovate), scabrous on midnerve, apex obtuse (rarely) or acute at apex, rarely short-awned; lemmas 2.3–6.0 mm long, narrowly ovate, ovate, or elliptic, the lateral nerves distinct and sometimes slightly excurrent, more or less sericeous on lateral nerves and the midnerve (hair tips rounded), apex truncate, obtuse, to acute or acuminate and sometimes bifid, awnless, mucronate, or awned to 3.5 mm; palea subequal or slightly exceeding lemma, more or less sericeous on nerves; apex acute or obtuse. Stamens 1, 2 or mostly 3; anthers 0.2–2.7 mm. Caryopses 1.0–2.4 ×0.7–1.2 mm, elliptic, ovate, or obovate in hilar profile, transversely elliptic to depressed obovate in transverse section, hilar groove lacking, smooth or sometimes slightly rugose, brown; pericarp weakly adnate to the endopserm.
Stems are hollow in Diplachne fusca (Canfield 1934; Ebinger and Carlen 1975; Brown 1975; Auquier and Sommers 1967; Valls 1978). When branching occurs in D. fusca it tends to be concentrated in the upper nodes (Valls 1978). Valls (1978: 33) observed that branching in D. f. subsp. uninervia tends to occur after the terminal inflorescence is fully developed, suggesting that branching is facultative and dependent on favourable growing conditions, presumably adequate soil moisture.
Flowering throughout the year in tropical latitudes; usually commencing early to mid-summer in temperate areas.
Native: Widespread and common to abundant in warm–temperate and tropical areas, between approximately 49°N and 40°S in the New World and 40°N and 42°S in Old World; mostly below 2000 m. Non-native: See under subspecies.
Malabar sprangletop; Chinese: shuang fu cao (双稃草) (and see others under subspecies).
Localised populations of the Diplachne fusca complex can be somewhat distinct morphologically from conspecifics occurring elsewhere, which is reflected in the many names that have been created to reflect such variation. However, all characters intergrade when considered globally (Snow 1997a), suggesting that the localised morphological variants do not merit recognition at the specific level. Field observations, herbarium work and multivariate statistical studies (Snow unpubl.) based on eleven population samples (n=20) from North America, Africa and Australia, which included over 80 morphometric traits, supported the recognition of four subspecies, which generally can be differentiated with little difficulty. These include: D. fusca subsp. fusca, a polymorphic Paleotropical taxon adventive in a few areas in the New World (Nicora 1995; Snow 2012); D. f. subsp. muelleri, known from much of the interior portions of Australia, particularly the Northern Territory; D. f. subsp. uninervia, native to the Neotropics but adventive elsewhere (e.g. Snow and Simon 1999) and D. f. subsp. fascicularis, native to the temperate and tropical regions of the New World.
Differentiating between subspecies can be particularly difficult in parts of California and Argentina, where D. f. subsp. fusca is adventive and sympatric with subspecies fascicularis and uninervia and in the Middle East and Australia (Western Australia, Queensland), where D. f. subsp. uninervia has become established (Snow and Simon 1999). It seems unlikely that D. f. subsp. fusca has persisted in California.
Specimens collected around wool combing mills in South Carolina in the United States by Ahles and associates in the 1950s and 1960s appear to be L. fusca subsp. fusca or occasionally subsp. muelleri, which likely arrived from wool exported by Australia to the Carolinas for the textile factories then common.
Key to subspecies of Diplachne fusca
- Snow, N; Peterson, P; Romaschenko, K; Simon, B; 2018: Monograph of Diplachne (Poaceae, Chloridoideae, Cynodonteae) PhytoKeys, (93): 1-102. doi
- Canfield R (1934) Stem structure of grasses of the Jornada Experimental Range. Botanical gazette (London) 95: 636–648. https://doi.org/10.1086/334434
- Ebinger J, Carlen J (1975) Culm morphology and grass systematics. Trans. Illinois State Acad. Sci. 68: 87–101.
- Brown W (1975) Variations in anatomy, associations, and origins of Kranz tissue. American Journal of Botany 62: 395–402. https://doi.org/10.2307/2442093
- Auquier P, Sommers Y (1967) Recherches histotaxonomiques sur le chaume des Poaceae. Bulletin of the Société royale de botanique de Belgique 100: 95–140.
- Valls J (1978) A biosystematic study of Leptochloa with special emphasis on Leptochloa dubia (Gramineae: Chloridoideae). PhD Dissertation, Texas A&M University, College Station.
- Snow N (1997a) Phylogeny and systematics of Leptochloa P. Beauv. sensu lato (Poaceae, Chloridoideae, Eragrostideae). Ph.D. dissertation, Washington University in St. Louis: Missouri.
- Nicora E (1995) Los géneros Diplachne y Leptochloa (Gramineae, Eragrosteae) de la Argentina y países limítrofes. Darwiniana 33: 233–256.
- Snow N (2012) Leptochloa P. Beauv. In: Zuloaga F Rúgolo Z Anton A (Eds) Flora Argentina, Vol. 3, Tomo 2. Graficamente Ediciones, Córdoba, 131–138.
- Snow N, Simon B (1999) Taxonomic status and Australian distribution of of the weedy neotropical grass Leptochloa fusca subsp. uninervia, with an updated key to Australian Leptochloa (Poaceae, Chloridoideae). Austrobaileya 5: 299–305.