Astragalus brauntonii Parish var. lativexillum A. E. Estrada, Rebman, C. González & Villarreal, 2022

Castillón, Eduardo Estrada, Rebman, Jon P., González, Carlos & Quintanilla, José Ángel Villarreal, 2022, Astragalus tijuanensis and Astragalus brauntonii var. lativexillum, a new species and a new variety in the genus Astragalus (Fabaceae) from extreme northwestern Baja California, Mexico, Phytotaxa 577 (1), pp. 1-13 : 6-9

Astragalus brauntonii Parish var. lativexillum A. E. Estrada, Rebman, C. González & Villarreal , var. nov. ( Fig. 4 and Fig. 5 )

Morphologically similar to Astragalus brauntonii Parish var. brauntonii , differing from this new variety by its shorter peduncles, fewer flowers per inflorescence, and narrower banner and wings.

Type:— MEXICO. Baja California (Municipio Tijuana ): along Boulevard 2000 between Rosarito and Tijuana, in the vicinity of the south side of the metropolitan area of the city of Tijuana , 32°20’11.008” N, 116°57’43.236” W, alt. 176 m, 7 June 2022, C. González 106 (Holotype MEXU!; isotype SD!) .

Herbaceous, caulescent, perennial with taproot. Stems several, hardened at base, straight, fistulated a little higher and striate, erect or ascending, up to 1.5 m tall, densely pubescent, villose to tomentulose, the trichomes, 1–1.7 mm long, entangled, white, wavy. Stipules 2.8–8 mm long, subulate to linear, abruptly widened at base, amplexicaul, decurrent, dorsally pubescent, embracing up to a half the circumference of the stem. Leaves gradually decreasing in size from base to apex, 5–15 cm long, leaflets 20–33 per leaf, 3–20 mm long, ovate, narrow elliptic to elliptic–obovate, acute to obtuse at apex, greenish to canescent, somewhat folded or flat, carinate adaxially by the midrib. Inflorescence, single or several at the top of the stems, the peduncles closely spaced, 0.7–1.5 cm, always shorter than leaf, peduncle up to 2 cm long, straight and erect, spreading to incurved, pubescent as stem, the floriferous axis up to 2 cm long in fruit, flowers 25 or less per raceme. Bracts 2.5–5.1 mm long, lanceolate, acuminate, straight to deflexed, densely villose– tomentose; pedicels ascending arched outward, 0.5–0.7 mm long; bracteoles absent. Flowers purple to pink–purple, dull, the calyx campanulate, 6.1–8.1 × 3–3.8 mm, the tube 3–4.1 mm long, the teeth 2.4–6 mm long, membranous or papery, villous with white trichomes or with white, black and darker colored fuscous ones mixed, or only with ones in the tube and fuscous ones at the teeth; the banner 9–12 × 6.9–7.5 mm, subentire to shallowly retuse, obovate, the wings 8.2–10.2 × 2–2.3 mm, elliptic–obovate, the claw 3.2–4.6 mm long, the blade 5.5–6.6. mm long, slightly incurved apically, narrow oblong–oblanceolate, auriculate basally; the keel 6.3–8.5 × 2.2–2.5 mm, the claw 3.3–4.3 mm long, the blade 3.7–4.5 mm, semi–obovate, incurved, apex rounded, auriculate; stamens 10–merous, diadelphous, 9 fused by their filaments into a white striped sheath 5–5.5 mm long, the free part 2.5–2.8 mm long, enfolding the ovary, the vexilar stamen 8.1–8.5 mm long, standing free; anthers yellow, elliptic, 0.6–7 mm long. Ovary unilocular, 6–9 ovulate, sessile, oblong, green, densely villous, 3–3.2 × 1 mm, the style linear, glabrous, style 6–6.5 mm long, pubescent at 2–3 mm of its base, then glabrate, incurved, stigma terminal, minute, glabrous, orange. Pod deflexed, 6.4–9 × 2.5–4 mm, caducous, sessile or upon a thin gynophore 0.7 mm long or shorter, the body oblong to ovate–oblong, plump, obtuse to cordate at base, apically acute in a incurved to subulate 1–1.5 mm long beak, openly triquetrous, ventrally keeled by the suture, the dorsal suture deeply grooved, the lateral faces widely rounded, the valves green, light–brown to stramineous, thinly fleshy, somewhat coriaceous to stiffly papery, villous to tomentose, with perpendicular reticulation below pubescence; septum 1–1.3 mm wide; seeds 1.2–2.2 mm long, brown to dark–brown, shallow wrinkled.

Distribution and habitat:— This is the first report of Astragalus brauntonii for Mexico, but it is represented as a new variety for this species. This new variety of A. brauntonii is separated approximately 240 km further south from the populations of this species present in Los Angeles County and adjacent counties in California. This new variety is only known from the type locality and two other populations in the area documented with inaturalist inaturalist. org/observations/120360892; inaturalist.org/observations/132226913) observations, at the southern edge of the city of Tijuana, Baja California ( Fig. 2 ), and it is coexisting with A. tijuanensis at the type locality. Both of these taxa are present in recently burned, disturbed, chaparral habitats on open gravelly or clayish hillsides, low slopes or flats, on clayish substrate.

Etymology:— The name of this new variety refers to the much wider banner petal of the flower for the new variety as compared to var. brauntonii .

Phenology:— According to the presence of reproductive structures on the type specimen, flowering likely occurred near the middle of May to early June and fruiting appears to be from early June to possibly early August.

Conservation status:— This new variety was discovered while surveying and documenting populations of a crossborder rare plant species called Deinandra conjugens as part of a binational collaborative project. This new taxon was only encountered in a single population at the type locality. Even though we documented other regional populations of Deinandra conjugens in the area, this new Astragalus was not found elsewhere. Furthermore, the populations and habitats for these new, rare taxa are within the Tijuana metropolitan area and this region is being strongly affected by human activity (personal observation). Thus, according to the GeoCAT, the extent of occurrences and the area of occupancy, which in this case is less than 1 km 2 and the default cell width of much less than 1 km, as recommended by the IUCN Red list guidelines ( IUCN 2017), A. brauntonii var. lativexillum should be placed in the category of critically endangered (CR), criterion B2ab (iii). Under the current conditions, Under current fire conditions, livestock impact and human settlement development that are being carried out in the area of distribution for these taxa, both new Astragalus taxa are facing a high risk of extinction. It is essential to continue botanical explorations in this region and adjacent areas in order to know if these new taxa are more widely distributed than currently known and to let the people of the region know of their existence, importance and promote their protection.

Discussion:— Most of the species of the sect. Inflati in Mexico are found in the Baja California region, and are easily distinguished from the rest of the other sections by their free stipules, relatively small flowers and unilocular, globose, obliquely–oblong, bladdery inflated or swollen, papery or slightly rigid, sessile and deciduous pod, and almost always the absence of the septum within the fruit. Morphologically, A. tijuanensis presents certain similarities with species from this section such as A. palmeri A. Gray (1868: 398) and A. deanei (Rydb.) Barneby (1958: 133) , but also physiognomically, it is somewhat similar to to A. pachypus Greene (1885: 157) (sect. Pachypodes (Jones) Barneby (1964: 487)) and A. deanei (sect. Inflati ) ( Table 1 ). Astragalus palmeri , A. deanei , and A. pachypus are distributed in the southern part of the state of California, USA, but only A. palmeri crosses the geopolitical border into Mexico and extends its distribution to almost the entire length of the state of Baja California. Astragalus tijuanensis and A. palmeri both occur in northern Baja California and are distributed in the regional arid ecosystems, sometimes in similar plant associations, but do not have sympatric ranges. Both species share several morphological characters in common, but certain easily distinguishable features are useful to discriminate them from each other. The most evident characters of A. tijuanensis are its thinly 0.1–0.3 mm long sparsely–strigulose pubescence on stems and leaves; greater number of leaflets per leaf (on average 21–29); leaflets up to 10 mm long, glabrate adaxially; 13–19 flowers per inflorescence; calyx teeth 0.7–0.9 mm long, and the banner 12.5–13 mm long. Astragalus tijuanensis has glabrous pods, and larger and fewer flowers per raceme than A. palmeri . The flowers of A. tijuanensis are white with purple tones, while in A. palmeri , the flowers are pink or pink–purple. Astragalus deanei is easily distinguished from A. tijuanensis by its white to ochroleucous flowers, much larger penduncles and racemes, and larger calyx and calyx teeth size, while A. pachypus has lemon–yellow or white flowers and a stipitate pod ( Table 1 ). It is interesting to note that the presence of Astragalus brauntonii is rare in Mexico, despite its relatively large size and its large and obvious foliage, easy to see in the field, growing in sites with some kind of disturbance in both, Mexico and USA. The short peduncles (2.4 cm long or shorter) and the abundant, small (6.1–8.1 mm long) and reflexed flowers, as well as the small reflexed semi–ovoid fruits with rigid valves of Astragalus brauntonii show a certain resemblance to that of Astragalus clevelandii Greene (1882: 121) , sect. Micranthi A. Gray (1864: 198) from the Coastal Ranges of northern California, but this new variety differs in having larger peduncles (10–30 cm long) and smaller flowers (5–6 mm long) than the latter species. The same characteristics of small flowers, long peduncles, and small, reflexed, ovoid, rigid and internally bilocular fruits are also shared with certain Mexican species of the sect. Micranthi A. Gray (1864: 198), but these are easily discernible by the presence of connate stipules.

Figures

FIGURE 2. Astragalus tijuanensis, part of the plant showing its leaves, inflorescences, flowers, and fruits.

FIGURE 4. Astragalus brauntonii var. lativexillum, A) Whole plant showing leaves, inflorescences, flowers and fruits. B) Stipule. C) Bract. D) leaflets showing the dense pubescence. E) inflorescence enlarged to see detail of the flowers. F) Flower. G) Calyx. H) Banner side view (left) and front view (right). I) Wing. J) Keel. K) Stamens. L) Ovary. M) Fruit. N) Seed.

FIGURE 5. A. brauntonii var. lativexillum part of the plant showing its leaves, inflorescences, and flowers.