Monographs Details: Astragalus micranthus Nutt. var. micranthus
Authors:Rupert C. Barneby
Authority: Barneby, Rupert C. 1964. Atlas of North American Astragalus. Mem. New York Bot. Gard. 13(1): 1-596.
Family:Fabaceae
Synonyms:Astragalus hartwegii f. pringlei Gand., , Astragalus rosei M.E.Jones, Atelophragma rosei (M.E.Jones) Rydb., Astragalus saltonis M.E.Jones, Hamosa saltonis (M.E.Jones) Rydb.
Description:Variety Description - Characters as given in the key [Key: "Plants varialbe in stature but often quite coarse, the stems (1.5) 2-5 dm. long; racemes 30-60-flowered, the asix 3-10 (16) cm. long in fruit; calyx (3.8) 4-5.6 mm. long, the teeth 1.1-2.2 (2.6) mm. long; banner (4.9) 5.1-7 mm. long; pod 8.5-13 mm. long; ovules 8-14 (16)"]; leaflets relatively numerous, mostly 21-31, varying from linear-oblanceolate to much broader; calyx-tube 2.1-3.2 mm. long, 2.1-2.8 mm. in diameter; banner (3.5) 4-6 mm. wide; wings (0.3 mm. shorter to 1.4 mm. longer) 6.1-7.9 mm. long, the claws (2.1) 2.3-3.5 mm., the blades 4-5.1 mm. long, 1.4-2 mm. wide; keel (4.8) 5-7 mm. long, the claws (2) 2.4—3.6 mm., the blades (2.7) 3.1—4.2 mm. long, (1.6) 1.9—2.4 mm. wide; pod 2.6-3.5 mm. in diameter, straight, slightly decurved, or gently incurved, the septum 0.7-1.5 mm. wide, sometimes nearly complete.

Distribution and Ecology - Sunny slopes and openings in pine forest, moist or dry mountain meadows, sometimes on damp hillsides among oaks, ± 8300-10,300 feet, common and locally plentiful in the mountains encircling the Valley of Mexico, from southern Hidalgo to northern Morelos and eastcentral Puebla.—Map No. 7.—June to December.

Discussion:

The pod of var. micranthus, as defined in these pages, is variable in length and correspondingly in ovule-number; and more strikingly so in curvature. Most commonly the pod is straight, more rarely it is a little arched downward, but especially when relatively long it may become gently incurved. An incurved pod is the one diagnostic feature of A. saltonis that was accordingly referred by Jones to his sect. Micranthi (a section based on A. micranthus Nutt., non Desv.) and by Rydberg to the genus Hamosa. Examining Jones’s key to the Micranthi (1923, p. 273), I find that his A. Seatoni was separated from A. saltonis by its shorter fruit (not over 7 mm. as opposed to 10 mm. or more long); but in the text (p. 281) the pod of A. Seatoni var. crucis was described as 8-12 mm. long, clearly falling into the range of A. saltonis. Rydberg evaded the responsibility of contrasting A. (Hamosa) saltonis with A. (Atelophragma) Rosei by placing them in separate genera; and by assigning Atelophragma Rosei and A. Seatoni to different sections defined in terms of flower-size (often incorrectly observed or reported), he avoided the problem posed by specimens with flowers falling between the critical upper limit of 5 mm. and lower one of 6 mm. in length. The combination A. Seatoni var. crucis was overlooked in North American Flora, but the isotypus at NY is annotated as A. Seatoni in Rydberg’s hand despite its flower-length in excess of 7 mm. The confusion in Rydberg’s mind as to the boundaries of these supposed species is especially evident in the light of annotations at US and NY. Thus he referred Nicolas & Arsene 105, with pod only 6 mm. long but relatively large flowers, to A. Rosei; and it would be possible to quote many equally contradictory examples.

The history of A. micranthus goes back to the earliest days of botanical exploration in Mexico. It was first collected by Sesse or Mocino (Herb. Sesse & Mocino Nos. 3637, 3746, MA; OXF) late in the XVIII century. It was under cultivation in Paris by 1809; unfortunately nothing was recorded as to the source of the seeds. It is possible, but by no means certain, that Phaca triangularis Zea ex Hornem., Hort. Hafn., Suppl. 83. 1819.—"Hab.--... intr. 1817 ex horto Gorinkiano sub hoc nomine."—(Astragalus triangularis (Zea ex Hornm.) DC., Prod. 2: 291. 1825) is an early synonym; a validating specimen is to be sought at Copenhagen.

Distribution:Hidalgo Mexico North America| Morelos Mexico North America| Puebla Mexico North America|