Poa thomasii Refulio, Syst. Bot. 37(1): 130. 2012.

Soreng, Robert J. & Peterson, Paul M., 2012, Revision of Poa L. (Poaceae, Pooideae, Poeae, Poinae) in Mexico: new records, re-evaluation of P. ruprechtii, and two new species, P. palmeri and P. wendtii, PhytoKeys 15, pp. 1-104 : 65-66

22. Poa thomasii Refulio, Syst. Bot. 37(1): 130. 2012. Fig. 3 C, D

Stenochloa californica ≡ Nutt., Proc. Acad. Nat. Sci. Philadelphia 4: 25. 1848. Dissanthelium californicum (Nutt.) Benth., Hooker’ s Icon. Pl. 4: 56. 1881. (non Poa californica Steud., Syn. Pl. Glumac. 1: 261. 1854.) Type: USA, California, Santa Catalina Island, Gambel s.n. (holotype: GH!; isotype: US! fragm. ex GH & rough drawing, herbarium label for drawing has "Nuttall script", and header "Coll. NUTTALL, Presented by Elias Durand, 1866").

Description.

Hermaphroditic. Annuals; tufted, tufts sparse, small, bases narrow, slender, bright green; tillers intravaginal (each subtended by a single elongated, 2-keeled, longitudinally split prophyll), without cataphyllous shoots, most shoots flowering. Culms (6-)10-46(-60) cm tall, erect or ascending, leafy, slender, leafy, terete, smooth; nodes 2-3, 2-3 exerted. Leaf sheaths slightly compressed, smooth, glabrous; butt sheaths thin papery, bases of butt sheaths glabrous; flag leaf sheaths up to 10 cm long, longer than those below it, margins fused ca. 50% their length, ca. equaling its blade; throats and collars smooth, glabrous; ligules 2-6 mm long, scarious-hyaline, abaxially smooth, glabrous, apex irregular, acute; blades 2.5-15(-20) cm long, (1-)2-4 cm wide, flat, thin, soft, abaxially smooth, margins lightly scabrous, adaxially smooth or slightly scabrous over costae, apex slender, not noticeably prow-tipped; flag leaf blades to 12 cm long. Panicles 5-16 cm long, erect, loosely contracted to open, slightly lax, moderately congested to sparse, with (10-)10-80 spikelets, proximal internode 2-4 cm long; rachis with 3-7 branches per node; primary branches sub-erect to ascending, slender, delicate, slightly angled, angles moderately scabrous; lateral pedicels to about 1/2 the spikelet length, moderately scabrous, prickles fine; longest branches 2-5 cm, with up to 12 spikelets some usually from near the base. Spikelets 2.5-5 mm long, cunniate at maturity, laterally compressed, not bulbiferous, green, sometimes anthocyanic, sub-lustrous; florets 2(-3), hermaphroditic; rachilla internodes terete, ca. 0.3 mm long, smooth, glabrous; glumes narrowly lanceolate, subchartaceous, green, lustrous, equal or subequal, both exceeding the florets, smooth, or keels scaberulous above, margins scarious, edges smooth, apex acuminate; lower glumes 3-4 mm long, 1-3-veined; upper glumes 3-4 mm long, 1-3-veined; calluses indistinct, glabrous; lemmas 1.5-2.2 mm long, 3(-5)-veined, ovate to elliptic, pale green, not lustrous, strongly keeled, keel smooth or sparsely scabrous above, surfaces minutely crisply appressed puberulent throughout the herbaceous portion, intermediate veins indistinct or absent, margins and apex narrowly scarious-hyaline, edges sometimes with a few hooks; apex obtuse to acute, sometimes denticulate in the upper margin; palea keels apically sparsely scabrous, medially glabrous or with a few hairs, surfaces glabrous or minutely pilose. Flowers mainly cleistogamous; lodicules 0.4 mm long, lanceolate, with a subapical lateral lobe; anthers 0.2(-0.4) mm long. Caryopses 1.1-1.2 mm long, elliptical in side-view, laterally compressed, sulcus indistinct, hilum ca. 0.15 mm long, elliptical. 2 n = unknown.

Distribution.

The species is found in the USA (California: Channel Islands) and Mexico (Baja California).

Ecology.

This annual species responds to winter and spring rains and fog on the Pacific Coastal Islands of southern California and Baja California Sur. Flowering Mar through May.

Conservation status.

Poa thomasii is listed as Federally Endangered in the United States, and it is rare and possibly extinct in Mexico.

Specimens examined.

Mexico. Baja California: Isla Guadalupe, 1875, E.Palmer 96 (MO).

Discussion.

From the time Bentham placed the species in Dissanthelium up to until Refulio-Rodríguez placed it in Poa ( 2012), it was known as Dissanthelium californicum ( Hitchcock 1913, Beetle 1987, Espejo Serna et al. 2000, Dávila Aranda et al. 2006, Refulio-Rodríguez 2007). DNA data confirm that all species of Dissanthelium are nested within Poa , and collectively are not monophyletic ( Refulio-Rodríguez et al. 2012). This species, which is morphologically and phylogenetically isolated from the core species of Dissanthelium placed in Poa sect. Dissanthelium (Trin.) Refulio, is endemic to the Channel Islands of southern California and Isla Guadalupe, Baja California. In Mexico it was collected on Isla Guadalupe by Dr. Edward Palmer in 1875 ( Gould and Moran 1981, Beetle 1987). It was thought to be extinct in the United States until it was rediscovered, after grazing pressures from feral goats and pigs, etc., were reduced or removed, on Santa Catalina Island in California ( McCune and Knapp 2008). Morphologically, it approaches Poa howellii Vasey & Scribn., a species of the adjacent lowlands in California (and north to British Columbia) that also reaches the Channel Islands.

Figures

Figure 3. A, B Poa bajaensis Soreng A habit B spikelet C, D Poa thomasii Refulio C habit D spikelet. A, B from Soreng (2002), drawn from holotype collection (Moran 15070) C, D from Refulio-Rodriguez (2007) as Dissanthelium californicum, originally drawn from Trask 324 in Hitchcock (1935).