Plateau rocktrumpet, flor de San Juan

Echites macrosiphon Torrey in W. H. Emory, Rep. U.S. Mex. Bound. 2(1): 158, plate 43. 1859; Macrosiphonia macrosiphon (Torrey) A. Heller; Telosiphonia macrosiphon (Torrey) Henrickson

Suffrutescent perennials, 1–4(–5) dm; rhizomes present. Stems densely eglandular-pubescent, especially on younger growth. Leaves opposite or rarely subopposite; petiole 3–6(–9) mm, densely pubescent; blade ovate, oblong-elliptic, or rarely orbiculate-reniform, 15–40(–60) × 10–35(–45) mm, sub­coriaceous, base cuneate, rounded, or cordate, margins revolute or not, apex acute to rounded or retuse, apiculate, surfaces densely white eglandular-pubescent abaxially, eglandular-pubescent adaxially. Cymes 1(very rarely 2)-flowered. Peduncles 0.5–1 mm, pubescent. Pedicels 4–9(–13) mm, pubescent. Flowers: sepals green, often streaked with red, oblong-ovate to oblong-lanceolate, 13–18(–25) × 2.5–5 mm, pubescent; corolla white, often tinged with pink or red, often becoming ferruginous upon drying, eglandular-pubescent abaxially and adaxially, tube 50–90 × 2–3 mm, throat 15–30 × 4–6 mm, lobes spreading, obliquely ovate, 25–40 × 18–35 mm. Follicles 100–150 × 3.5–4 mm, pubescent. Seeds 5.5–7 × 1.5–2 mm.

Flowering spring–fall; fruiting summer–fall. Desert grasslands on limestone or igneous soils; 300–1700 m; Tex.; Mexico (Chihuahua, Coahuila, Durango, Zacatecas).

J. Henrickson (1996b) noted that along the eastern margin of its range, Mandevilla macrosiphon appears to grade into M. lanuginosa, both species forming small plants with densely pubescent foliage. The two species can usually be easily distinguished on the basis of growth habit, M. macrosiphon exhibiting a suffrutescent habit with new shoots of the season arising from a root crown or from lower branches of the previous season, while M. lanuginosa is a shrub with new shoots developing from its upper stems.