Festuca of North America


S. G. Aiken, M. J. Dallwitz, C. L. McJannet, and L. L. Consaul

Festuca sororia Piper


Contrib. U.S. Natl. Herb. 16: 197. 1913. F. subulata var. sororia (Piper) St.-Yves, Candollea 2: 285. 1925. Type: U.S.A. Arizona: Rincon Mountains in ravines, alt. 225 m. August and Sept. 1891, G. C. Nealley 177. Holotype: US! Isotypes: GH! NY!)

F. fratercula auct. non Rupr. ex Fourn. Max. Pl. 2: 124. 1886.

Habit. Plants deep green (leaves mainly on the culms), (60–)75–130(–150) cm high, not densely tufted, tiller bases not stiffly erect (stout perennials, Cronquist et al. 1977), bases purplish, horizontal rooting stems present (short). Vegetative shoots arising outside, or breaking through the base of existing sheaths.

Vegetative morphology. Sheaths with trichomes (retrorsely scaberulous), not conspicuous at the base of the plant, splitting between the veins, open more than half their length. Collars glabrous. Auricles absent. Ligules 0.5–1.2(–1.5) mm long, ciliate (sometimes sparsely, the cilia are longer than the ligule membrane). Leaf blades 10–25 cm long, more or less lax. Adaxial blade surfaces glabrous or with trichomes (on the margins and veins, if present), abaxial blade surfaces glabrous. Leaf blades flat, 3–7(–10) mm wide. Veins 15–25 (distance between the veins more than 2 times the width of the veins). Adaxial to abaxial sclerenchyma strands present. Abaxial sclerenchyma poorly developed, in discrete, relatively narrow strands opposite the veins. Uppermost culm leaf sheaths not inflated. Flag leaf blades 10–17 cm long. Culm nodes becoming exposed, 2–3; internodes glabrous.

Floral morphology. Inflorescence 10–20(–40) cm long (somewhat nodding). Inflorescence branches at the lowest node (1–)2(–3), spreading (capillary and often reflexed), 4–10(–12) cm long. Rachis rounded in cross section or angular in cross section, trichomes mainly on the ridges or trichomes over the entire surface. Spikelets aggregated towards the ends of the branches; 3–6 on the longest branches; (7–)8–12 mm long, 2–4 mm wide. Proliferating spikelets absent (not recorded for this taxon). Florets 3–4(–5). Glumes unequal, with trichomes (scabrous on midvein), margins not ciliate. First glume (1.5–)3–4 mm long (narrowly lanceolate), veins 1. Second glume shorter than the first lemma, (3.5–)5–6 mm long (lanceolate), veins (1–)3. Rachilla internodes antrorsely scabrous (sparse). Lemma callus not elongated (but with a tuft of hairs similar to the callus of F. subuliflora). Lemma (5–)6.5–8.5(–9) mm long (narrowly acuminate), with 5 distinct veins in dorsal view or nerveless in dorsal view or sometimes with only the centre vein distinct, with trichomes, trichomes over the entire surface; apex entire. Lemma awn present or absent. Lemma awn (0–)0.2–1.5(–2) mm long (when applicable). Palea (6–)7–8 mm long (slightly exceeding the lemma), distinctly pubescent between the keels. Lodicules without marginal teeth, glabrous or ciliate, 1.2–1.5 mm long. Anthers 1.8–2.3 mm long. Ovary apex pubescent. Caryopsis 4–6 mm long.

Cytology. 2n = 28.

Habitat and Distribution. Native; alpine. Moist, shady areas from middle to subalpine elevations. Southwestern USA: Ariz.; Rocky Mountains USA: Colo., Utah; South Central USA: N. Mex.

Classification. Subg. Subulatae Tzvelev, sect. Subulatae Tzvelev.


Piper (1913) commented that the North American grass referred to as F. fratercula Rupr. ex Fourn. is not that plant at all, but an unnamed species, which he proceeded to name, F. sororia.

This is a rare species that occurs in Colorado, Arizona and New Mexico in mountain ravines. Cronquist et al. (1977) described it as occurring in open woods and meadows from middle elevations to the subalpine zone and added a record from southern Utah (Abajo Mts., Rydberg and Garrett 9852).

Aiken et al. (1997) mapped the distribution of species that they placed in subg. Subulatae, sect. Subulatae and noted that in this section F. sororia is the most distinct species, but unlike the other taxa it has never been placed in a distinct subgenus. The species has a limited distribution in the south-western United States that suggests it may have been separated from its near relatives and evolved in isolation, or that the species may have nearer relatives in Mexico.

This species has been looked for at the type locality, but not found there recently (personal communication, J. & C. Reeder 1997).


• Isotype specimen: GH. Annotated as "Isotype specimen of F. sororia Piper, Aug. 27 1947. C.A. Taylor Jr." Main label reads "177, from the United States National Herbarium, F. fratercula Rupt? Det. 7500 ft. In ravines. Locality Rincon Mountains, Arizona. Collector G.C. Nealley, Aug. & Sept. 1891. rel." GH. • Isotype specimen: NY. Annotated as "Isotype specimen of F. sororia Piper, Aug. 27 1947. C.A. Taylor Jr." Main label reads, "177, from the United States National Herbarium, F. fratercula Rupt? Det. 7500 ft. In ravines. Locality Rincon Mountains, Arizona. Collector G.C. Nealley, Aug. & Sept. 1891." NY. • Distribution map

The interactive key provides access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting specified attributes, and summaries of attributes within groups of taxa.

Cite this publication as: ‘Aiken, S.G., Dallwitz, M.J., McJannet, C.L. and Consaul, L.L. 1996 onwards. Festuca of North America: descriptions, illustrations, identification, and information retrieval. Version: 19th October 2005. http://delta-intkey.com’. Aiken, Dallwitz, McJannet, and Consaul (1997) should also be cited (see References).