Dalea neo-mexicana var. megaladenia

  • Title

    Dalea neo-mexicana var. megaladenia

  • Author(s)

    Rupert C. Barneby

  • Scientific Name

    Dalea neomexicana var. megaladenia Barneby

  • Description

    4c. Dalea neo-mexicana (Gray) Cory var. megaladenia Barneby

    (Plate XXXII)

    Often more robust than var. neo-mexicana, the stems up to 3.5 dm long; leaves 2-4.5 cm long, the leaflets shaped and marginally undulate as in var. neo-mexicana but glabrous or nearly so above; peduncles 1-4 cm, and raceme-axis 2-6 cm long; calyx 4.7-6.9 mm, its tube 2.1-2.5 mm, and teeth 2.5-4.4 mm long; petals ochroleucous or stramineous sometimes lilac-tipped, rarely blue; 2n = 16 (Mosquin). —Collections: 17 (i).

    Sandy and gravelly flats, dry rubbly hillsides, on limestone and gypsum, sometimes on dunes, 1100-1270 m (3650- 4230 ft), locally abundant but confined to interior desert basins of w. Coahuila between lat. 26° 30' and 28° 30' N, s.-w. around the s. margin of Bolson de Mapimi into convergent comers of Chihuahua (mpo Jimenez) and Durango (mpo Gomez Palacio), there reaching s. to 25° 40', and n.-w. just into the corner of Chihuahua below the Big Bend of Rio Bravo (mpo Manuel Benavides) at nearly 29° N. — Flowering June to November, following rains. — Representative: Chihuahua: s.-e. of San Carlos, road to Providencia, Johnston & Mueller 101 (MICH, TEX); n.-w. of Escalon, Correll & Johnston 21,453 (RENNER). Coahuila: w. of Castillon, R. M. Stewart 555 (GH); Matrimonio to Americanos, I. Johnston 9374 (GH, TEX); Llano de Guaje, R. M. Stewart 1150 (GH); s.-e. of San Jose on road to San Antonio de los Alamos via Zenzontle, Johnston & Mueller 976 (MICH, TEX); Mohovano, Purpus 4484 (F, UC); s. of Est. S. Fernando, toward Sa. Mojada, M. C. Johnston et al. 10861 (NY); n. end of Bolson de los Lipanes, Johnston & Mueller 1237 (TEX); Sa. de los Remedios n.-e. of Tlahualilo, Henrickson 12188 (TEX). Durango: base of Sa. de Mapimi near Dinamita, Ripley & Barneby 14,207 (CAS, DAO, GH, MEXU, MICH, NY, US).

    Dalea neo-mexicana (Gray) Cory var. megaladenia (with large glands) Barneby, var. nov., a var. neo-mexicana quoad foliorum ambitu cuneato-obcordato marginibus undulatis similis sed foliolis superne glabris vel ad marginem parce pilosulis, glandulis pedicellum fulcrantibus maximis (ad0.5-0.7 mm usque longis), calycisque dentibus saepissime brevior- ibus (dorsali 2.5-4.4 mm longo) abstans.— Coahuila: sand hills on road from Guimbalete s.-e. to Acatita via Laguna del Rey, sept 17, 1942, coll. Reynaldo Santos under direction of Robert M. Stewart, distrib. Stewart 2646. — Holotypus, GH; isotypus (fragm), NY.

    The material listed as var. megaladenia is somewhat heterogeneous in detail, but differs collectively from var. neo-mexicana in the green or glaucescent foliage, the leaflets glabrous or only marginally pubescent above, in the massive glands at base and apex of the pedicels, and in the relatively short calyx-teeth. In general the plants are coarser than the average var. neo-mexicana, with larger leaves and longer, somewhat looser racemes. The petals vary in color, according to different collectors "blue" (the type), "light lemon" or "yellow" (Stewart), or as seen in northeast Durango ochroleucous faintly tipped or tinged with dull pinkish lilac. Because of the thin pubescence combined with large glands and sometimes blue petals, I suspected at first that the entity represented a series of hybrids involving D. neo-mexicana and D. lachnostachya, the ranges of which coincide about the edge of that of var. megaladenia. But where the two species are sympatric and even closely associated in parts of trans-Pecos Texas no hybrids have ever been seen. It seems entirely more likely that D. neo-mexicana has given rise under the extremely severe conditions of the bolson region in the Chihuahuan Desert to a series of modified populations not yet stabilized or uniform nor, probably, detached genetically from the parental stock. A collection from gypsum in the Conchos valley in the latitude of Ciudad Chihuahua (Johnston 8300, GH) which I have referred to var. neo-mexicana has relatively large glands in the inflorescence; and another population on the Rio Grande in Webb County, Texas, already mentioned particularly under var. neo-mexicana, has with the vesture of the latter the short calyx-teeth of var. megaladenia.