Muhlenbergia diandra (R.W. Pohl) Columbus, Aliso 28: 66. 2010 (21 May).

Peterson, Paul M., Herrera Arrieta, Yolanda, Lobo Cabezas, Silvia & Romaschenko, Konstantin, 2023, Taxonomic revision of Muhlenbergia (Poaceae, Chloridoideae, Cynodonteae, Muhlenbergiinae) in Central America: phylogeny and classification, PhytoKeys 230, pp. 1-106 : 1

6. Muhlenbergia diandra (R.W. Pohl) Columbus, Aliso 28: 66. 2010 (21 May).

Fig. 5C-G

Pereilema diandrum R.W. Pohl, Novon 2(2): 102. 1992. Type: Costa Rica, Heredia: Puente Mulas, S of San Antonio, canyon of Río Virilla, 850 m, 28 Nov 1968, R.W. Pohl & G. Davidse 11482 (holotype: ISC-277884!; isotypes: CR-46688!, K-000308951 [image!], MO-356265 fragm. ex ISC!, US-3054594!). ≡ Muhlenbergia diandra (R.W. Pohl) P.M. Peterson, Amer. J. Bot. 97(9): 1543. 2010 (1 Sep), isonym. Basionym.

Description.

Caespitose annuals. Culms 35-90 cm tall, erect to somewhat decumbent and rooting at the lower nodes, smooth and glabrous below the nodes; internodes 1-2 mm diameter, glabrous or slightly scabrous, often reddish. Leaf sheaths shorter than the internodes, scabrous or smooth; prophyll s 2-3 cm long, prominent, bifid; ligules 0.7-1 mm long, membranous, thick, apex truncate; blades 9-22 cm long, 5-9 mm wide, flat, scabrous, auriculate near base, the auricles 1-2 mm long, ciliate, clasping. Panicles 10-22 cm long, 1-2.5 cm wide, cylindrical, solitary, exserted or included in the sheaths below; primary branches 1-3.5 cm long, ascending mostly appressed, spreading up to 70° from the culm axis with dense fascicles of florets; pedicels 0.1-0.3 mm long, the spikelets arising just above the sterile spikelets or bristles, the bristles 3-5 mm long. Spikelets (fertile) 1.8-2.8 mm long; glumes 0.7-1.5 mm long, subequal, oblong to ovate, 1-veined, awned, the awns 1.5-4 mm long; lemmas 1.8-2.6 mm long, lanceolate, scabrous 3-veined, awned, the awns 10-24 mm long, straight, callus hairy, the hairs 0.6-1 mm long; paleas 1.8-2.8 mm long, slightly longer than the lemma, apex bidentate; stamens 2, anthers 0.8-1 mm long, often purple. 2 n = 80 ( Pohl and Davidse 1971).

Distribution.

The species is endemic to Costa Rica and is known from Provincias Alajuela, Heredia, Puntarenas, and San José ( Peterson et al. 2001; Morales 2003).

Ecology.

Muhlenbergia diandra occurs on dry to moist roadsides and disturbed sites on the margins of humid forests; 500-1800 m.

Comments.

Muhlenbergia diandra differs from M. pereilema in having wide leaf blades 4-9 mm long (2-3 mm wide in M. pereilema ), lemmas with straight awns (flexuous in M. pereilema ), and chromosome number ( Davidse and Pohl 1992; Morales 2003). This species probably forms a clade with M. beyrichiana Kunth, M. pereilema , and M. plumiseta Columbus within M. subg. Muhlenbergia ( Peterson et al. 2021).

Muhlenbergia beyrichiana is only known to occur in Brazil, Ecuador, and Peru as determined here. Earlier, it was reported in México and Central America but these are in error ( Espejo Serna et al. 2000; Lægaard and Peterson 2001; Peterson et al. 2001, 2018).

Specimens examined.

Costa Rica. Hoffmann 465 ( US); Río Tiliri, A. Tonduz 3121 (MO, CR). Alajuela: Poás, Carrillos de Poás, A.M. Brenes 14606 (CR, US); Naranjo, puente sobre el Rio Colorado donde el Tropical Bungee, B. Hammel 20587 (INB, CR); Naranjo, open areas on upper slopes of Cerro Espíritu Santo, 1-3 km SW of Naranjo, A.S. Weston et al. 3852 (CR). Heredia: Puente de Mulas, S of San Antonio, Canyon of the Río Virilla, R.W. Pohl & G. Davidse 11482 (MO, CR). Puntarenas: Monteverde, 10 km S Monteverde on road to Inter-American Highway, area of spring, W. Haber & W. Zuchowski 9639 (MO, INB); Cordillera de Tilarán, 10 km SW Santa Elena on road from Monteverde to Inter American Highway, dry ridges and cut banks, W. Haber & W. Zuchowski 10305 (MO, INB, US). San José: San Francisco de Guadalupe, A. Tonduz 9817 (CR, MO, US); Mora, Llano Grande Puriscal, O. Jiménez 890 ( US, CR); Orillas del camino a San Juan, O. Jiménez 161 ( US); vicinity of Santa Maria de Dota, P.C. Standley 41769 ( US), 43224 ( US), 44066 ( US); Bordes del rio Torres, San Francisco de Guadalupe, A. Tonduz 7198 ( US).

Figures

Figure 5. A, B Muhlenbergia cenchroides (Humb. & Bonpl. ex Willd.) P. M. Peterson A habit B spikelets C-G Muhlenbergia diandra (R. W. Pohl) Columbus C habit D ligule with auricles E glumes F floret G stamens and pistil. A, B drawn from S. Beck 7464 used in Renvoize (1998) C-G drawn from P. C. Standley 44066 (US- 1307162)