Agrostis microphylla Steud., Syn. Pl. Glumac. 1: 164. 1854.

Vigosa-Mercado, J. Luis, Delgado-Salinas, Alfonso, Alvarado Cardenas, Leonardo O. & Eguiarte, Luis E., 2023, Revision of the genus Agrostis (Poaceae, Pooideae, Poeae) in Megamexico, PhytoKeys 230, pp. 157-256 : 157

11. Agrostis microphylla Steud., Syn. Pl. Glumac. 1: 164. 1854.

Figs 4J , 5J , 23

Agraulus brevifolius Nees ex Torr., Pacif. Railr. Rep. 4: 154. 1857, nom. inval., pro syn.

Agrostis virescens Kunth var. microphylla (Steud.) Scribn., Circ. Div. Agrostol. U.S.D.A. 30: 2. 1901.

Agrostis exarata Trin. var. microphylla (Steud.) Hitchc., Amer. J. Bot. 2: 303. 1915.

= Agrostis microphylla Steud. var. intermedia Beetle, Bull. Torrey Bot. Club 72(6): 547. 1945. Type. USA. California: Lake County, 2.9 miles north of Middletown, 11 May 1943, J.T. Howell 18063 (holotype: AHUC (AHUC9939 [image!]); isotype: CAS (CAS0000198 [image!])).*

Type.

America septentrionalis, D. Douglas s.n. (not located).

Description.

Plants annual, caespitose. Tillers absent. Culms 4-25 cm long, erect, nodes 1-3, glabrous, internodes glabrous. Leaves usually mostly cauline; sheaths 1.5-8 cm long, longer or shorter than the internodes, glabrous; ligules 1-5 mm long, longer than wide, dorsally scaberulous, apices acute to truncate, erose, often lacerate; blades 1-8 cm long, 0.5-2.5 mm wide, flat, scaberulous on both surfaces. Panicles 1-9 cm long, 0.5-1.4 cm wide, contracted, dense, spiciform, linear to lanceolate, sometimes interrupted at the base, sometimes partially included in the upper sheaths; branches appressed, rebranching from below mid-length, scaberulous, with spikelets almost to the base, inferior branches 0.6-2.5 cm long; pedicels 0.3-2.5 mm long, appressed, scaberulous. Spikelets 3-4.5 mm long, greenish to stramineous; glumes unequal, lanceolate, apices long acuminate or awned, 1-veined, scaberulous on the keel, sometimes also on the body, lower glume 3-4.5 mm long including the awn, upper glume 2.5-4 mm long; callus pubescent, with two bunches of trichomes; lemmas 1.5-2 mm long, elliptic, apices 2(-4) toothed, 5-nerved, veins inconspicuous or prominent distally, awned about mid-length, awn 3.5-6 mm long, inserted 0.8-1 mm above the base, geniculate; paleas absent or up to 0.2 mm long, veinless, glabrous; anthers 3, 0.4-0.5 mm long. Caryopsis 1-1.5 mm long, elliptic; endosperm soft. 2n= 56 ( Harvey 2007).

Anatomy and micromorphology.

Leaf blades flat in transversal section; adaxial furrows shallow, wide; adaxial ribs rounded; keel absent; first order bundles circular in outline, sheath interrupted adaxially and abaxially, abaxial and adaxial sclerenchyma in girders, narrowing towards the bundle; second order bundles circular in outline, sheath interrupted abaxially, abaxial and adaxial sclerenchyma in strands; intercostal sclerenchyma absent; leaf margins with small sclerenchyma caps, rounded; colorless cells absent (Fig. 22D-F ). Lemmas with transversal thickenings irregular to oblong, wider than the unthickened portions of the wall; prickle hairs scarce to abundant (Fig. 7J ).

Distribution and habitat.

Agrostis microphylla is distributed from British Columbia, Canada, to the northern peninsula of Baja California, Mexico ( Harvey 2007). In the study zone, this species has been collected in the Mexican state of Baja California (Fig. 18E ), where it grows in stream edges and vernal pools, between 37-315 m a.s.l. (Fig. 9N ). It has also been reported from the state of Baja California Sur, but the database record linked to this report has no images ( GBIF 2023c), and thus we were unable to confirm its identity.

Phenology.

Specimens with spikelets have been collected from April to June (Fig. 10N ).

Commentaries.

It has been reported for other regions that the culms can reach 45 cm long, panicles up to 12 cm long, spikelets up to 5 mm, and awns up to 8 mm ( Harvey 2007).

Agrostis microphylla is one of the few annual Agrostis species. It is often confused with the smaller forms of A. exarata , from which it differs in the annual habit, spikelets of 3-4.5 mm long and lemmas with an awn of 3.5-6 mm long (vs. perennial plants, spikelets of 2-2.5 mm, lemmas unawned or with an awn up to 3 mm long in A. exarata ), as well as the leaf blade anatomy and lemma micromorphology.

Conservation status.

Agrostis microphylla is apparently a rare species in the study zone. It is represented by only four collections, with no populations occurring in protected areas. The EOO is 897 km2 and the AOO is 12 km2. Following the IUCN criteria, the preliminary assessment category is Endangered (EN).

Specimens examined.

Mexico. Baja California: Municipio Ensenada , 5 km SSO of Johnson Ranch, N of Cabo Colonet, [31.05833°N, 116.29167°W], 37 m alt., 31 May 1980, R. Moran 28447 (SD), 28643 (MEXU [*,**], SD); Guadeloupe [Guadalupe] ranch, [32.0754°N, 116.6217°W, 315 m alt.], 6 Apr 1886, C.R. Orcutt s.n. (US); arroyo Agua Caliente, [32.11163081°N, 116.4650486°W], 300 m alt., 25 June 1980, R. Rosiñol 10 (MEXU [*, **]) .

Figures

Figure 4. Florets of Agrostis species observed with SEM A A. bourgaei B A. calderoniae C A. capillaris D A. elliottiana E A. exarata F A. ghiesbreghtii G A. gigantea H A. hyemalis I A. laxissima J A. microphylla K A. pallens L A. perennans M A. scabra N A. stolonifera O A. subpatens P A. subrepens Q A. tolucensis R A. turrialbae S A. variabilis. Scale bars: 0.3 mm.

Figure 5. Calluses of Agrostis species observed with SEM A A. bourgaei B A. calderoniae C A. capillaris D A. elliottiana E A. exarata F A. ghiesbreghtii G A. gigantea H A. hyemalis I A. laxissima J A. microphylla K A. pallens L A. perennans. Scale bars: 50 μm.

Figure 7. Lemma surface of Agrostis observed with SEM A A. bourgaei B A. calderoniae C A. capillaris D A. elliottiana E A. exarata F A. ghiesbreghtii G A. gigantea H A. hyemalis I A. laxissima J A. microphylla K A. pallens L A. perennans. Scale bars: 15 μm.

Figure 9. Elevation histograms of Agrostis species A all records B native species C introduced species D A. bourgaei E A. calderoniae F A. capillaris G A. elliottiana H A. exarata I A. ghiesbreghtii J A. gigantea K A. hyemalis L A. idahoensis M A. laxissima N A. microphylla O A. pallens.

Figure 10. Phenology histograms of Agrostis species A all records B native species C introduced species D A. bourgaei E A. calderoniae F A. capillaris G A. elliottiana H A. exarata I A. ghiesbreghtii J A. gigantea K A. hyemalis L A. idahoensis M A. laxissima N A. microphylla O A. pallens.

Figure 18. Map of known geographic distribution of Agrostis species, based on herbarium specimen data A A. gigantea B A. hyemalis C A. idahoensis D A. laxissima E A. microphylla F A. pallens.

Figure 22. Leaf blade anatomy in transversal section of Agrostis species, in general view, and details of lateral bundles. A - C A. laxissima D - F A. microphylla G - I A. pallens J - L A. perennans. Scale bars: 0.1 mm.

Figure 23. Agrostis microphylla A whole plant B ligular area C spikelet D floret, abaxial view. Based on Rosinol 10 (MEXU). Scale bars: 3 cm (A); 1 mm (B, C); 0.5 mm (D).