Eragrostis

Eragrostis Wolf

Eragrostis is a large genus of ca. 350 species, mostly confined to tropical and warm-temperate regions of the world. None is native in Belgium. Several species are economically important, either as ornamentals, as fodder, for soil stabilisation, etc. Some have become noxious environmental or agricultural weeds.

Species of Eragrostis – mostly of African or Australian origin – were among the most typical wool aliens in the valley of river Vesdre near Verviers. In addition to the species treated in detail in this account more than 20 additional species were recorded in the past (but none survived).

Taxonomically, Eragrostis is a surprisingly complex genus. The delimitation of taxa in some species groups is often critical. This particularly seems to be the case in areas where closely related taxa grow sympatrically which might suggest introgression. In parts of southern Europe (for instance in northern Italy) the boundaries in the Eragrostis pilosa-complex (E. diffusa Buckley, E. multicaulis, E. pectinacea, E. pilosa s.str.) are often seriously blurred. In Belgium, on the contrary, where Eragrostis pilosa s.str. is an exceptional and ephemeral alien, the delimitation from the widely naturalised E. multicaulis always is straightforward. In the same complex speciation seems to be going on: Eragrostis albensis H. Scholz was described as a neo-endemic from river banks in Central-Europe (see also below), although more recent studies suggest that it may be conspecific with the Asian E. imberbis (Franch.) Prob. (Seregin 2012). Glandular Eragrostis pilosa (with minute depressions on at least the leaf sheath keels) should be looked for, especially in the eastern portion of Belgium. Such plants belong to the Eurasian Eragrostis amurensis Prob. (syn.: E. voronensis H. Scholz) and are rapidly expanding in eastern Europe (Seregin 2012). Other critical species groups include the Eragrostis mexicana-complex (with E. mexicana s.str., E. neomexicana and E. virescens in Belgium) and the E. curvula-complex (with, among others, E. chloromelas, E. curvula s.str. and E. lehmanniana Nees). Additional morphological and molecular studies are needed to resolve the relationships in these complexes.

1. Leaf margins, leaf sheaths, pedicels and/or spikelets with numerous or scattered raised crateriform glands. Annual grasses === 2

1. Raised crateriform glands absent (glandular tissue might be present on leaf sheaths, near the culm nodes, below the inflorescence or elsewhere). Annual or (more rarely) perennial grasses === 3

2. Middle cauline leaf sheaths glabrous. Pulvini usually hairy. Caryopsis globose, ca. as long as wide. Upper glume usually 3-nerved throughout. Spikelets usually more than 2 mm wide, often some with more than 20 florets === Eragrostis cilianensis

2. Middle cauline leaf sheaths almost always long hairy. Pulvini usually glabrous. Caryopsis ovoid, longer than wide. Upper glume usually 1-nerved or with 2 additional nerves at base only. Spikelets usually less than 2 mm wide, with much less florets === E. minor

3. Perennial grasses, densely caespitose. Leaves setaceous with long filiform apex. Caryopsis 1,3 mm long, bicoloured. Anthers ca. 1 mm long === E. curvula

3. Annual grasses, easily uprooted. Leaves never setaceous with a filiform apex. Caryopsis smaller (or, if as large, than never bicoloured). Anthers at most 0,3 mm long === 4

4. Caryopsis with a ventral groove. Stem often with an irregular ring of glandular tissue below the nodes === 5

4. Caryopsis flat, without a ventral groove. Stem never with glandular tissue below the nodes === 7

5. Spikelets usually less than 1,5 mm wide. Lemmas less than 2 mm long. Stem usually without glandular tissue below the nodes === E. virescens

5. Spikelets usually wider than 1,5 mm. Lemmas more than 2 mm long (or, if less, then stem with glandular tissue below the nodes) === 6

6. Stem always with an irregular ring of glandular tissue below the nodes. Plant usually tall, often more than 80 cm tall. Leaves up to 12 mm wide. Lemmas less than 2 mm long === E. neomexicana

6. Stem never (or very rarely) with glandular tissue below the nodes. Plant usually smaller, often less than 50 cm tall. Leaves up to 6 mm wide. Lemmas more than 2 mm long === E. mexicana

7. Caryopsis more or less pyriform, whitish to pale brown, 1-1,5 mm long, turgid. Lemmas 1,8-3 mm long, acute to shortly acuminate; lower glume 1-2 mm long. Plant often tall, commonly more than 60 cm === E. tef

7. Caryopsis elliptical to ovate, never whitish, at most 0,8 mm long. Lemmas smaller, 1,2-1,8 mm long, obtuse to subacute. Plant usually much smaller, rarely exceeding 50 cm === 8

8. Lower glume 0,5-1,5 mm long, at least ½ as long as adjacent lemma. Lowermost inflorescence branches solitary or paired. Periligular zone (collar region) of the uppermost leaves pilose. Spikelets usually at least 1,5 mm wide === E. pectinacea

8. Lower glume 0,3-0,7 mm long, less than ½ as long as adjacent lemma. Lowermost inflorescence branches solitary to (sub-) verticillate. Periligular zone of the uppermost leaves glabrous or pilose. Spikelets usually less than 1 mm wide === 9

9. Lowermost inflorescence branches (sub-) verticillate. Periligular zone of the uppermost leaves always with some long hairs === E. pilosa

9. Lowermost inflorescence branches solitary. Periligular zone (collar region) of the uppermost leaves mostly glabrous === 10

10. Inflorescence branches smooth (rarely very slightly scabrous in upper branches). Panicle pyramidal to oblong, longest branches in the lower ¼ of the panicle, usually not exceeding 5 cm. Pedicels usually shorter than the spikelets === E. multicaulis

10. Inflorescence branches scabrous. Panicle rhomboid in outline, the longest branches in the middle of the panicle, up to 12 cm long. Pedicels of lateral spikelets often longer than the spikelets === E. albensis

Additional aliens: Eragrostis advena (Stapf) S.M. Phillips (syn.: Thellungia advena Stapf) (Aus., wool alien), E. alveiformis Lazarides (Aus., wool alien), E. atrovirens (Desf.) Trin. ex Steud. (syn.: E. biformis (Kunth) Benth.) (Afr., trop. As., wool alien), E. bahiensis Schrad. ex Schult. (S-Am., wool alien), E. barrelieri Daveau (Medit., wool alien), E. bicolor Nees (Afr., wool alien), E. brownii (Kunth) Nees (Aus., wool alien), E. chloromelas Steud. (Afr., wool alien), E. ciliaris (L.) R. Brown (Afr., vector unknown), E. dielsii Pilger (Aus., wool alien), E. elongata (Willd.) Jacq. (syn.: E. diandra (R. Brown) Steud.) (Aus., trop. As., wool alien), E. lacunaria F. Muell. ex Benth. (Aus., wool alien), E. leptocarpa Benth. (Aus., wool alien), E. leptostachya (R. Brown) Steud. (Aus., wool alien), E. neesii Trin. (S-Am., wool alien), E. nigra Nees ex Steud. (As., wool alien), E. obtusa Munro ex Ficalho et Hiern (syn.: Briza geniculata Thunb.) (Afr., wool alien), E. papposa (Duf.) Steud. (Medit., Afr. As., wool alien), E. parviflora (R. Brown) Trin. (syn.: E. pelucida (R. Brown) Steud.) (Aus., wool alien), E. nigricans (Kunth) Steud.) (N-Am., wool alien), E. plana Nees (syn.: Diplachne hackeliana Thell.) (Afr., wool alien), E. planiculmis Nees (Afr., wool alien), E. procumbens Nees (Afr., wool alien), E. rotifer Rendle (syn.: E. margaritacea Stapf) (Afr., wool alien) and E. trichophora Coss. et Durieu (syn.: E. atherstonei Stapf) (Afr., wool alien).