Hesperolinon micranthum (A.Gray) Small, 1907

González-Velasco, Juan, Burgos-Hernández, Mireya, Galván-Escobedo, Iris G. & Castillo-Campos, Gonzalo, 2022, Taxonomic update of the flax family in Mexico, Phytotaxa 549 (2), pp. 141-184 : 143-146

Hesperolinon micranthum (A.Gray) Small , (1907i: 85.) ( Fig. 1 ).

Type:— UNITED STATES OF AMERICA. California: Mariposa County, Mt. Bullion , Bolander 4854 (holotype GH!, isotypes DS, UC!) .

Linum micranthum A. Gray (1868: 333) .

Description: — Herbs, 5–50 cm in height, glabrous to sparsely puberulent at the base; stems slightly decumbent, smooth, branched from the base, glabrous; stipular glands generally present at the base. Leaves entire, basal leaves in whorls, distal leaves alternate; linear or closely oblong, (5.5)10.0–20.0(–30.0) × (0.3)1.5–2.5(–3.0) mm; sessile, apex acute to obtuse, glabrous, stipular glands present only in basal leaves. Inflorescence in a cymose panicle, pedicels 3.9– 14.6(–30.0) mm long, sometimes longer in the fruit; bracts 0.9–1.3 mm long, margin entire, apex acute; sepals entire or with minute marginal glands, lanceolate, 1.0–3.0 × 0.6–0.9 mm, apex slightly acuminate, glabrous; petals white to light pink, oblanceolate, 1.5–3.5 mm long; stamens 1.5–2.5 mm long; anthers purple or dark purple, 0.3–1.0 mm long; styles 3, 0.5–1.0(–2.0) mm long, stigmata capitate; ovary 3 or 6-locular for the presence of false septa. Fruit yellow, 1.3–1.5 × 1.3–1.4 mm, pericarp thin, apex acute, dehiscent into 6 segments; seeds 6, 1.1–1.3 × 0.4–0.6 mm.

Distribution: — United States of America; in Mexico, in northern Baja California ( Fig. 2a ).

Habitat and ecology: — Cypress-juniper forest and chaparral shrubland. Elevation 50–2000 m. Common in serpentine soils in the California biogeographic province.

Phenology: —Flowering and fruiting in May–October.

Note: —Although the species is not endemic to Mexico, its distribution is restricted to the California biogeographic province ( Delgadillo 1998, Morrone 2019). Hesperolinon micranthum is the only species in the genus reported ( Springer 2009, Schneider et al. 2016, Jepson eflora 2019) and corroborated in this study, with a distribution range stretching to Mexico. According to the material reviewed, the species is clearly distinguished from the species in the genus Linum distributed in Mexico by the number of carpels, styles, and stigmata, as well as by the dehiscent fruit.

Conservation status: —According to IUCN Red List Categories and Criteria ( IUCN 2019), H. micranthum is Endangered (EN) (B1 + 2ac(iii)). Its extent of occurrence (EOO) is less than 5,000 km 2 (1,751.668 km 2) and its estimated area of occupancy (AOO) is 12 km 2. This species presents a restricted distribution, only known in Baja California in Mexico. Additionally, its habitat has been subjected to multiple anthropogenic pressures ( Morrone 2019), and may face major risks.

S pecimens examined: — MEXICO. Baja California: Ensenada, Rancho Caliente , 22 May 1971, I.L. Wiggins 21556 ( ENCB!) ; Tecate, Cerro Jesús María , 770 m, 30°31’00’’N, 116°49’00’’W, 9 May 1970, R. Moran 17565 ( ENCB!) ; Tecate, Cerro Matomí , 1300 m, 30°23’00’’N, 115°06’00’’W, 4 May 1973, R. Moran 20820 ( ENCB!) .

Figures

FIGURE 1. Hesperolinon micranthum. A.Aspect general of the plant; B. Leaf; C. Flower; D. Filament and anther; E. Styles and stigmata; F. Seed; G. Fruit. Illustrated by Lizbeth Pérez Lucas, based on I.L. Wiggins 21556.

FIGURE 2. Geographic distribution in the Mexican territory of: A. H. micranthum, L. aristatum, L. berlandieri var. filifolium, L. longipes, and L. rupestre; B. L. australe, L. australe var. glandulosum, L. flagellare, L. nelsonii, and L. usitatissimum. Maps by Ma. Isabel Olivares.