Gonolobus, Michaux, 1803

Carnevali, Germán, Romero-González, Gustavo A., Tapia-Muñoz, José Luis, Ramírez-Morillo, Ivón M., Ramírez-Díaz, Claudia J., Cetzal-Ix, William, Stefano, Rodrigo Duno De & Romero-Soler, Katya J., 2022, Twice lost, twice found: A new species of Gonolobus (Apocynaceae: Asclepiadoideae) with a reappraisal of the genus in the Yucatan Peninsula Biotic Province, Phytotaxa 530 (2), pp. 141-162 : 144-145

Key to the Gonolobus of the Yucatan Peninsula Biotic Province

1. Leaves elliptic, shortly and abruptly cordate at the base; adaxial surface glabrous, restricted to the Guatemalan Petén .................... ........................................................................................................................................................................ Gonolobus glaberrimus

1. Leaves ovate, ovate elliptic, or oblong-ovate, always sharply and conspicuously cordate basally; abaxial surface variously pubescent at least over the nerves; plants from several areas of the YPBP........................................................................................2

2(1). Corolla lobes very narrow, narrowly to linear triangular, at least 10 times longer than wide; leaves essentially glabrous or with scattered trichomes applicate on the nerves, base lobate, sinus between basal lobes shallow and broad; plants usually from seasonally flooded forests or mangrove associations................................................................................... Gonolobus cteniophorus

2. Corolla lobes broader, usually elliptical or oblong elliptical, no more than 5–6 times longer than wide; leaves always conspicuously pubescent, sinus between basal lobes from deep with lobes overlapping or parallel to shallow; plants usually from non-flooded areas (usually seasonally dry forests to tropical dry forests)..............................................................................................................3

3(2). Corolla abaxially pubescent with trichomes 0.05–1.5 mm long ........................................................................................................4

3. Corolla abaxially glabrous or rarely with a few trichomes at the apex of the lobes ..........................................................................6

4(3). Corolla conspicuously reticulate on the adaxial surface, with conspicuously barbate lobes along the right margin, trichomes 2–3 mm long, yellow; leaves fundamentally glabrous; plants from disturbed environments growing and flowering in the sun; internodes in the flowering branches or stems relatively short (petioles as long or longer) with several nodes and flowers blooming simultaneously..................................................................................................................................................... Gonolobus barbatus

4. Corolla concolorous or inconspicuously reticulate, right margin with a pubescence similar to that of the corolla blade, trichomes 0.05–0.1 mm long, green, whitish or translucent; leaves pubescent; plants from mature or secondary forests in seasonally dry to humid areas, flowering exposed or in the shade; internodes in the flowering branches or stems longer than the petioles with only a few nodes and flowers blooming simultaneously ..............................................................................................................................5

5(4). Leaves with deeply cordate bases, basal lobes deep, subparallel to often overlapping; corolla flat; corolla lobes 15–18 × 4.7–6 mm oblong triangular to oblong, acute to narrowly acute, lobes dextrogyrously angled at the distal half forming an angle of 30–35° to the general axis of the flower, with a dark-purple to almost black longitudinal, callose band along the proximal 2/3 on the right side of the lobes; faucal corona almost black, conspicuous; dorsal anther appendages simple ................................. Gonolobus caamalii

5. Leaves with shallowly cordate bases, basal lobes never overlapping; corolla shortly campanulate proximally; corolla lobes 6.9– 10.7 × 4–5.1 mm, ovate to elliptic with obliquely acute to obtuse, not conspicuously angled, lacking a longitudinal, callose, black band; faucal corona white, inconspicuous; dorsal anther appendages with two conspicuous lobes.................. Gonolobus fraternus

6(3). Calyx lobes patent, broadly triangular, 8.1–19 × 5.8–11 mm; corolla lobes asymmetrically elliptic, 18–34 × 6–12 mm, acuminate; leaf abaxially conspicuously pale-yellow-green with brownish nerves, noticeable even on dry material......... Gonolobus leianthus

6. Calyx lobes conspicuously reflexed in anthesis (noticeable in live and herbarium material), triangular to triangular-elliptic, 11–14 × 3.8–5.5 mm; corolla lobes oblong, 14.7–20.3 × 3–3.5 mm, acute; leaf abaxially slightly paler green that adaxial surface, nerves not conspicuous ..................................................................................................................................................................................7

7(6). Corolla green; plants from the south of the YPBP (southern Campeche and Quintana Roo, Northern Belize and the Guatemalan Petén)................................................................................................................................... Gonolobus stenanthus subsp. stenanthus

7. Corolla very dark brown, almost black; plants from the northeastern portion of the YPBP (Yucatán state, NE Quintana Roo) ........ ......................................................................................................................................... Gonolobus stenanthus subsp. yucatanensis