Marsdenia, Brown, 1810

Carnevali, Germán, Trejo-Torres, Jorge Carlos, Juárez-Jaimes, Verónica, Duno, Rodrigo, Tapia-Muñoz, José Luis, Ramírez-Morillo, Ivón M. & Cetzal-Ix, William, 2016, Marsdenia calichicola (Apocynaceae), a narrow endemic, endangered new species from the Mexican Yucatan Peninsula, Phytotaxa 270 (2), pp. 146-154 : 152

Key for the species of Marsdenia from the Yucatan Peninsula Biotic Province

1. Inflorescences laxly paniculate, often exceeding the subtending leaves, always very much exceeding the petioles, composed of long (25–70 mm), glabrous, filiform peduncles and branches each topped by an umbel with 3–5 long pedicelled flowers; pedicels 15–25 mm long.................................................................................................................................................................. M. laxiflora

– Inflorescences congested, paniculiform or umbelliform, usually shorter than subtending leaves, shorter, subequaling to slightly longer than petioles, composed of one or few, short, thick, variously pubescent peduncles plus branches (1–16 mm long) each topped by few- to many-flowered fascicles or subumbels, pedicels 1.5–10.0 mm long....................................................................2

2. Leaves narrowly elliptic or oblong, glabrous; colleters absent at leaf base; corolla greenish to extremely dark purple, almost black ................................................................................................................................................................................... M. mayana

– Leaves elliptic, ovate, broadly ovate to suborbicular, always pubescent; colleters present at leaf base; corolla white, pale yellow, greenish white, or white with red stripes............................................................................................................................................3

3. Leaves broadly elliptic to suborbicular, almost as broad as long, base always cordate, sinus 1/10 of total leaf-blade length, inconspicuously ferruginous-puberulent; lateral veins 7–8 pairs; laminar colleters 6–24..................................................... M. hiriartiana

– Leaves elliptic to ovate, almost twice as long as wide, base acute, truncate, obtuse to shallowly lobed, when rarely lobed then sinus not exceeding 1/20 of total leaf-blade length, glabrous or with various indument types but never ferruginous-puberulent; lateral veins 3–7 pairs; laminar colleters 2–10..............................................................................................................................................4

4. Leaves oblong-elliptic to broadly elliptic, 3.0–4.5 × 1.5–2.4 cm, base cuneate; lateral veins 3-4 pairs; petioles 3–5 mm long; corollas white with 3-4 red longitudinal stripes that cover 2/3 of total corolla lobe length; sinuses of the corolla lobes with thickened, cushion-like, densely pubescent calli ............................................................................................................................ M. calichicola

– Leaves elliptic to ovate, 2.5–19.0 × 1.2–11.5 cm, base obtuse, truncate to shallowly lobed; lateral veins 4–7 pairs; petioles exceeding 5 mm; corolla pale yellow or greenish-white, never with red longitudinal stripes covering 2/3 of total corolla lobe length; sinuses of the corolla lobes lacking calli............................................................................................................................................5

5. Leaves ovate, 2.5–7.8 × 1.2–5.9 cm; corolla subrotate, lobes adaxially appressed-pilose excepting a glabrous margin, abaxially glabrous or (more rarely) sparsely appressed-pilose; apex of the style rostrate................................................................. M. coulteri

– Leaves elliptic to ovate, 5.5–19.0 x 3.3–11.4 cm; corolla campanulate or tubular, lobes adaxially papillose to glabrous, abaxially glabrous; apex of the style variously shaped but never rostrate.........................................................................................................6

6. Leaf apex acuminate; petiole 1.4–6.0 cm long, appressed-tomentulose; pedicels 1.5–4.5 mm long; calyx lobes 1–2 × 0.8–1.5 mm; corolla campanulate, tube 1–2 mm long, lobes 1.5–2.5 × 0.8–1.5 mm, adaxially papillose; gynostegium stipitate, 0.2–0.4 mm tall; corolline corona absent; follicles 4.5–8.5 × 2–3 cm .................................................................................................... M. gualanensis

– Leaf apex abruptly acuminate (more rarely rounded); petiole 0.9–3.8 cm long, glabrous or tomentulose; pedicels 4–10 mm long, calyx lobes 2.5–4 x 2–3 mm; corolla tubular-salverform, tube 2.5–3 mm long, lobes 2.5–3.5 × 1.5–2.5 mm, adaxially glabrous; gynostegium sessile, 2 mm tall; corolline corona present; follicles 10.5–13.0 × 3.5–4.0 cm........................................ M. propinqua