Linum puberulum A. Heller 1896

Linum puberulum A. Heller (1896: 627). (Fig. 9c).

Type:— UNITED STATES OF AMERICA. New Mexico: Santa Fe to the Cimarron River, Fendler 85 (holotype US!, isotypes GH!, K!, MO, NY, PH, UC).

Linum rigidum var. puberulum Engelmann (1852b: 25).

Cathartolinum puberulum Small (1907j: 80).

Mesynium puberulum (Engelm.) W.A.Weber (1984: 3).

Description: — Herbs, annual or perennial, 5–25 cm in height, densely gray-puberulent to the inflorescence, root thick; stems ascending, branched from the base, puberulent. Leaves, basal ones entire, occasionally opposite; distal ones sparsely glandular-dentate, alternate; linear, (5.4)7.0–20.0 × 0.6–1.5 mm, sessile, apex acuminate, whitish tip, 1-nerved, scariose, glabrous, stipular glands prominent at the base. Inflorescence a cymose panicle, pedicels 3.4(5.0–)–9.5(–10.0) mm long; bracts 2.5–7.3 mm long, margin glandular-dentate, apex acuminate, stipular glands prominent at the base; sepals persistent, lanceolate, (3.1)4.5–7.0 × 1.1–1.5 mm; margin glandular-dentate, sometimes scariose; apex acute to acuminate, 3-nerved, puberulent at least in the central nerve, stipular glands absent; petals yellow-orange to salmon, with reddish to dark-red base; obcordate or widely obovate, 7.0–14.0 mm long; stamens 4.0–7.0 mm long; anthers 0.6–1.4 mm long, yellow; staminodia absent; styles fused to near the apex, 3.0–7.0 mm long; stigmata capitate, dark brown. Fruit ovoid, yellow, 1.7–4.2 × 1.8–4.0 mm, glabrous, pericarp thick, apex obtuse, dehiscent into 5 segments; seeds narrowly ovate, reddish-brown, 2.3–3.0 × 0.9–1.3 mm.

Distribution: — United States of America; in Mexico, in Coahuila and Sonora (Fig. 5b).

Habitat and ecology: —Thornless or sub-thornless small-leaved shrubland, sandy arid desert vegetation. Elevation 273–1287 m. Phaeozem, Lithosol, Regosol, and Xerosol soil types.

Phenology:—Flowering and fruiting in April–October.

Note: —This is the only species in the genus in northwest Mexico with puberulent stems, corolla almost hemispherical in shape, and styles attached almost to the apex. It should be noted that some specimens are puberulent only in the basal part; in these cases, the dark brown capitate stigmata help differentiate it from L. vernale, which is glabrous and with which it might be confused.

Conservation status: —Although the EOO of L. puberulum is 32,537.414 km 2, its distribution in Mexico is not continuous affecting the polygon that encompasses the occurrence of this species. Therefore, based on its AOO (16 km 2) and its localities known (<5) in the country, the species can be considered as EN (B2ac(iii)). However, this species is widely represented in the United States of America, highlighting that this evaluation corresponds only to Mexico.

Specimens examined: — MEXICO. Coahuila: Acuña, 72 km al noroeste de Ciudad Acuña, 596 m, 29°34’01”N, 101°42’04”W, 23 April 2017, J.A. Encina et al. 5830 (ANSM!, MEXU!); Acuña, Rancho Los Ángeles, 560 m, 29°34’02”N, 101°37’12”W, 18 April 2017, J.A. Encina et al. 5750 (MEXU!); Piedras Negras, 13.47 km al sureste de la Ciudad de Piedras Negras, 273 m, 28°31’17”N, 100°29’35”W, 24 April 2016, J.A. Encina et al 5323 (ANSM!). Sonora: Agua Prieta, Northeast of Sierra Anibácachi, 1287 m, 31°13’59”N, 109°37’53”W, 23 April 2004, A.L. Reina et al. 300 (MEXU!).