Linum aristatum Engelmann (1848: 101)

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 : 147

Linum aristatum Engelmann (1848: 101) . ( Fig. 3a ).

Type:— MEXICO. Chihuahua: Near Carizal south of El Paso , Wislizenus 101 (holotype MO!, isotype GH!) .

Cathartolinum aristatum Small (1907a: 83) .

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

Description: — Herbs, annual, 10–45 cm in height, glabrous, main root thick; stems extended, ascending, rigid, broomshaped, striate, branched from the base, glabrous. Leaves entire, alternate; basal leaves sometimes opposite; linear, (4.8)5.0–20.0 × 0.3–1.1 mm, sessile; apex acute to acuminate, tip whitish to translucent; 1-nerved, membranous, glabrous; stipular glands present at the base, black. Inflorescence a cymose panicle, pedicels thin, 6.2–34.0 mm long; bracts 5.5–9.0 mm long, apex acuminate, margin glandular-dentate, stipular glands absent; sepals deciduous, linearlanceolate, scariose, 6.4–7.5 mm long, glandular-dentate, apex smoothly attenuated; 3-nerved, central nerve evident; without stipular glands; petals yellow to yellow-orange, obovate, 8–12 mm long, glabrous; stamens 5–7 mm long, glabrous; anthers elliptical, 0.7–1.1(1.2) mm long, yellow; staminodia absent; styles fused to near the apex, 4.5–7.0 mm long; stigmata capitate, yellow. Fruit ellipsoid, yellow, clearly longer than wide, 3.5–4.0 × 2.5–3.0 mm, glabrous, pericarp thin, apex obtuse, dehiscent into 5 segments; seeds elliptical, dark brown, 2.5–3.0 × 0.8–1.0 mm.

Distribution: — United States of America; in Mexico, in Chihuahua, Coahuila, and Tamaulipas ( Fig. 2a ).

Habitat and ecology: —Cypress-juniper forest, oak forests, oak-pine forests, thornless or sub-thornless smallleaved shrubland, grasslands, pine forests, vegetation of sandy arid deserts. Elevation (300) 1100–3100 m. Dry sandy soils of the Phaeozem, Lithosol, Luvisol, Regosol, Vertisol, and Xerosol types.

Phenology: —Flowering in March–August; fruiting in August–November.

Note: — Linum aristatum is easily distinguished from the rest of the species with dehiscence into 5 segments for having pale ellipsoid fruits and thin pericarp, in addition to narrow and smoothly attenuated sepals.

Conservation status: —According to IUCN Red List Categories and Criteria ( IUCN 2019), L. aristatum is EN (B1 + 2ab(iii)), with an EOO <5,000 km 2 (52.886 km 2) and AOO <500 km 2 (12 km 2). The areas where this species occurs in Mexico have been used for tourist-recreational purposes and overgrazing, industrial development, and urban growth have also been reported ( Fernández et al. 2014).

Specimens examined: — MEXICO. Chihuahua: Along hiway 45, 112 miles N of Gallego, 1250 m, 18 July 1975, K.L.Wallace et al. 136 ( ENCB!) ; Juárez , 4.8 miles S of Samalayuca, 1275 m, 31°18’00”N, 106°29’00”W, 19 August 1971, J. Henrickson 5780 ( MEXU!) ; Juárez , 5 km N of Samalayuca, 1250 m, 31°24’30”N, 106°27’36”W, 28 October 1972, T.L. Wendt et al. 9922 ( MEXU!) . Coahuila: Gravelly mesas near Díaz , 742 m, 29°10’24.81”N, 101°36’0.97”W, 17 April 1900, C.G. Pringle 8312 ( MEXU!) . Tamaulipas: Nuevo Laredo, Sandy upland fourteen miles south of Nuevo Laredo , 141 m, 27°20’25.11”N, 99°36’19.33”W, 24 March 1944, N.T. Heard & F.A. Barkley 14604 ( MEXU!) .

Figures

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.

FIGURE 3. A. Linum aristatum; B. Linum australe; C. Linum berlandieri var. filifolium; D. Linum cruciata. Photographs by José Luis Colin.