Astragalus comonduensis A. E. Estrada, Rebman & Villarreal, 2019

Castillón, Eduardo Estrada, Rebman, Jon P. & Quintanilla, José Ángel Villarreal, 2019, Astragalus comonduensis and Calliandra pilocarpa (Fabaceae), two new species from Baja California Sur, Mexico, Phytotaxa 391 (1), pp. 57-68 : 59-62

Astragalus comonduensis A. E. Estrada, Rebman & Villarreal , sp. nov. ( Fig. 1. A–L )

Morphologically similar to Astragalus aridus A. Gray (1864: 223) , but differs in its erect habit, strigulose pubescence, mucronate and adaxially glabrate leaflets, shorter and narrower calyx with both white and black intermixed trichomes, color of flowers, degree of pod inflation, consistency and pubescence type on fruit surfaces, ovule number, and seed size.

Type:— MEXICO. Baja California Sur (Municipio Comondú): Llano La Laguna: Sierra de la Giganta Region, north of San José de Comondú near Rancho Palo Fierro ; southern portion of the llano, 26°08’19.9’’N, 111°46.1’19.6’’ W, alt. 505 m, 9 March 2016, J. Rebman 31220 with R. Domínguez Cadena & F. Pio León (Holotype SD 255900 !; isotype HCIB) .

Plant annual, caulescent. Stems erect, up to 45 cm long, striate, green or green-reddish, turning purple when dry, strigulose, the trichomes 0.2–0.4(–0.5) mm long, white, straight, appressed; stipules free or some amplexicaul by half to three-quarters of stem´s circumference, straight or basally oblique, 2–3 × 1–2 mm, ovate, gradually to abruptly acute at the apex to triangular-lanceolate, brown-yellow, green or reddish-tinted, strigulose abaxially, the trichomes 0.2–0.5 mm long, white with some black ones intermixed, glabrate adaxially, margins ciliate, straight or reflexed with age. Leaves (2–)4.2–7.3(–7.9) cm long, short petioled, the petiole 3–10 mm long; leaflets (13–)14–17(–21), (3.2–)4.2– 9.5(–17) × 1.4–4 mm, elliptic to elliptic-obovate, petiolulate, petiolule 0.3–0.7 mm long, orange to reddish, glabrate to sparsely strigulose, base acute, apex mucronate, mucro 0.1–0.3 mm long, glabrate adaxially, strigulose abaxially with mainly white trichomes¸ leaf rachis strigulose to densely strigulose on young leaves, trichomes white or white with a few black ones intermixed. Inflorescences in axillary racemes, (6.4–) 6.5–8.9 cm long, peduncles 3.8–4.9 cm long, erect, ascending, 10°–20° angled from stem, sparsely strigulose, with both white and black trichomes; floriferous axis 1.6–4.4 cm long, 4–9 flowered; flowers mostly ascending, and remaining so in fruit, rarely spreading; bracts 1.1–1.5 mm long, lanceolate to triangular-lanceolate, green, sparsely strigulose, with white and black trichomes intermixed abaxially, glabrous adaxially; pedicels 1–2 mm long, slightly thickened in fruit, sparsely strigulose similar to bracts, persistent after fruit falls, bractlets 0. Flowers 5–5.5 mm long; calyx 2–2.8 × 1–1.2 mm, campanulate, the tube 2–2.8 mm long, slightly inequilaterous, more deeply recessed behind the banner, strigulose, with white and black trichomes, the teeth 0.8–1.2 mm long, lanceolate to triangular-lanceolate, green, green-reddish to reddish, sparsely strigulose as the tube; petals purple-lavender, some flowers becoming bluish with age, the banner sessile, 4.5–5 × 2.1–2.2 mm, elliptic to elliptic-obovate, sometimes longitudinally inequilaterous, a side wider than the other, folded near the middle, and margins folded again backward, slightly bent backward from the keel, distally recurved 25°–50° from the vertical, apically retuse, the notch 0.2–0.3 mm deep; wings 4.2–4.6 mm long, the claw 2–2.1 mm long, the blade 2.3–2 × 1.3–1.4 mm, oblong, oblique, half-obovate, unguiculate, and auriculate, the apex rounded; the keel 3.9–4 mm long, the claw 1.8–1.9 mm long, the blade 1.9–2 × 1.2–1.3 mm, strongly incurved, half obovate, apically triangular, the beak curved slightly backwards, unguiculate and auriculate. Stamens 10-merous, diadelphous, 9 fused by their filaments into a white, slightly striped sheath 2.9–3.1 mm long, the free portion 0.8–1 mm long, enfolding the ovary, the vexilar stamen 3.8–3.9 mm long, standing free; anthers spherical or almost so, 0.3–0.4 mm diameter, yellow to yellow-orange. Ovary unilocular, 0.9–1.2 mm long, sessile, densely strigulose, trichomes white, style 0.9–1.2 mm long, incurved, glabrate, stigma terminal, minute, glabrate, ovules 7–9. Pod ascending when young and remaining so, sessile, obliqueovoid, subglobose, bladdery-inflated, 10–14 × 6–10 mm, basally somewhat cuneate, distally abruptly contracted in a triangular, slightly laterally compressed, 2–3 mm long beak, ventrally shallow sulcate by the filiform suture and it less convex than the also filiform dorsal suture, the valves little flattened dorsoventrally, sparsely and minute strigulose, the trichomes 0.1–0.3 mm long, tan to reddish, becoming purple when dry, subdiaphanous to opaque; seeds 2.1–2.5 mm long, opaque, smooth, light-brown to brown.

Distribution and habitat: —As currently known, there are only two specimens of Astragalus comonduensis , both collected at Llano La Laguna located in the Sierra La Giganta region, north of San Jose de Comondú in Baja California Sur ( Fig. 4 ). Based on the collection descriptions, this species grows with vegetation dominated by Datura wrightii Regel (1859: 193) , Heliotropium procumbens Miller (1768: 10) , Ambrosia confertiflora DC. (1836: 526) , Prosopis articulata S. Watson (1889: 48) , Parkinsonia aculeata L. (1753: 375), Eclipta prostrata L. (1771: 286), and Nicotiana glauca Graham (1828: 2837) , in wet muddy soil near the water’s edge along the banks of ephemeral lakes. One of the specimens (Rebman 31220), was very large and loaded with fruits and only portion of it was collected for herbarium specimen. The other specimen (Domínguez 3140) collected in 2002, we don’t know how many individuals were there at that time.

Etymology: —The name of the species refers to the municipality of Comondú, where the plant is only known to occur.

Phenology: —With only two specimens of Astragalus comonduensis currently known, phenological information is rather limited. However, based on the phenological conditions of these specimens, flowering apparently occurs from February to March, and fruiting is likely from March to June. Samples of Astragalus aridus , A. insularis Kellogg (1884: 6) , and A. idrietorum Barneby (1964: 703) distributed in adjacent or near areas to the type locality were examined in other herbaria (BCMEX, CAS, CFNL, NYBG and SD), in order to ensure the correct determination and discrimination of these with the new species (Appendix I).

Additional specimens examined (paratypes): — MEXICO. Baja California Sur (Municipio Comondú): La Laguna, al norte de San José de Comondú, 26°06’48.2’’N, 111°46’38.2’’W, alt. 443 m, 14 March 2002, M. Domínguez L. 3140 (SD 157777, HCIB 16970).

Notes: —The morphological characteristics of this species, such as free stipules and inflated unilocular fruit, make it part of Astragalus sect. Inflati A. Gray (1864: 213) . It also has several morphological characteristics that place it in Astragalus subsect. Aridi M.E. Jones (1923: 92) . These include: annual habit, leaflets 7–21, racemes with 2–10 flowers, small purple flowers, 7–22 ovules, and persistent, sessile, erect and unilocular pod. Within Astragalus subsect. Aridi , the annual species Astragalus aridus A. Gray (1864: 223) is the only other species characterized by having erect fruits and few (3–7) ovules while the rest of the species in the group show extended or declined fruits, and a greater number of ovules. Astragalus comonduensis characteristically exhibits erect fruits and few ovules (7–9). However, there are several differences between these two annual species. 1. Astragalus comonduensis reaches up to 42 cm high and the stems are erect, not eventually decumbent and trailing as in A. aridus ; 2. The pubescence of A. comonduensis is strigulose with 0.2–0.4(–0.5) mm long, straight, white, appressed trichomes, not silky or satiny-canescent, with ascending 0.6–1.1 mm long trichomes as in A. aridus ; 3. The leaflets of Astragalus comonduensis are mucronate and glabrate adaxially, not equally pubescent on both leaf surfaces and never mucronate as in A. aridus . 4. In respect to the perianth, the calyx of A. comonduensis is shorter (2–2.8 mm long) and narrower than that of A. aridus (3.2–4.4 mm long), plus it exhibits both white and black intermixed trichomes unlike the uniformly white trichomes of A. aridus . 5. Both species have small flowers, but A. comonduensis has purple-lavender petals, while A. aridus has been reported to have whitish, pink-lilac or flesh colored petals. 6. Also, the keel of the new species has a very distinctive small curved backward beak which is absent in A. aridus . 7. In addition to these features, there are marked differences regarding the pods, with those of A. comonduensis being completely inflated, bladdery, proportionally wider, shiny, and not laterally compressed (not even minutely), opaque to sub-diaphanous, and minutely-strigulose, while the pods of A. aridus are little inflated, but not bladdery, laterally compressed at both ends, and strongly so at the apex, with the valves being densely white canescent to strigulose-pilose, papery, and opaque. 8. Furthermore, A. comonduensis has a greater number of ovules (7–9) per ovary and smaller seeds (2.1–2.5 mm long) that are smooth and light brown, while A. aridus usually contains 3–7 ovules per ovary and 9. A. aridus has larger seeds (2.7–3.7 cm long). Astragalus insularis and A. idrietorum are also found on the Baja California peninsula, and are physiognomically somewhat similar to A. comonduensis , but these two species can easily be distinguished by their much longer perianth parts. Astragalus insularis also has reddish-purple flowers that turn violet when dry, and fruits that are spreading or reflexed with age. Astragalus idrietorum has a perennial versus annual habit, and racemes with (8)10–20 flowers versus only 4–9 flowers found in A. comonduensis . Although both Astragalus comonduensis and A. idrietorum have ascending pedicels, A. idrietorum is easily differentiated by its larger calyx size (5–5.2 mm long), flower color (pink-purple, drying violet with age) and larger petal sizes (banner 6.5–9 mm long, wings 5.7–7.9 mm long, and keel 5.7–7.4 mm long). Table 1 show the most significant morphological differences between Astragalus aridus and A. comonduensis .

Figures

FIGURE 1. Astragalus comonduensis, A) Picture of the whole plant. B) Stipule. C) Leaf. D) Leaflet. E) Wing petal. F) Keel petal. G) Banner petal. H) Androecium with nine filaments united. I) Vexilar stamen. J) Fruit. K) Seed. L) Complete flower. Illustration by Callie Mack.

FIGURE 4. Distribution of Astragalus comonduensis and Calliandra pilocarpa in Baja California Sur, Mexico.