No key was found for the requested taxon, but its parent (Matelea) is keyed as shown below.

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Key to Apocynaceae

Apocynaceae

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(c) Cenoteando - CC-BY-SA
1 Plant erect or trailing (but not twining), herbaceous or woody.
(c) Cenoteando - CC-BY-SA
  2 Plant a woody shrub, subshrub, or woody vine (trailing or climbing, but not twining).
(c) Shorma, Jared - CC-BY
(c) Menchetti, Stefano - CC-BY-SA
      4 Fruit follicles; [waif]
(c) Bradley, Keith
      4 Fruit drupes; [native and non-native]
(c) Bradley, Keith
(c) Bradley, Keith
        5 Leaves lanceolate; corolla white, salverform, < 1 cm long; fruit white; [rare native, s. FL]
(c) Hannan-Jones, Martin - CC-BY
(c) mikami-kun - CC-BY
        5 Leaves linear; corolla yellow, funnelform, ca. 5 cm long; fruit green to brown; [non-native, s. TX and FL peninsula]
    3 Leaves opposite to subopposite or whorled.
(c) Burger, Margaret - CC-BY-SA
          6 Plants armed, the stems with stout, bifurcated spines
          6 Plants unarmed, the stems without spines.
(c) Danielson, Erik
(c) Bradley, Keith
             7 Plant primarily trailing, rhizomatous, and suffrutescent, < 4 dm tall (usually becoming a "ground-cover"); leaves narrowly to broadly ovate; flowers blue, lavender, or white
             7 Plant erect, > 4 dm tall (2-5+ dm tall in Mandevilla, but plants not trailing and lacking rhizomes) or trailing and obviously woody (Allamanda, which has yellow flowers); leaves either lanceolate or elliptic (oblanceolate to obovate in Allamanda cathartica and Tabernaemontana); flowers yellow, white, pink, or red.
(c) Bradley, Keith
(c) Wong, Michelle - CC-BY
               8 Flowers white, pink, or red; shrubs or trees (shorter shrubs [2-5 dm tall] in Mandevilla; [non-natives, except Mandevilla].
(c) Wong, Michelle - CC-BY
(c) Hill, Sonnia
                 9 Flowers cream-colored, long salverform (the floral tube 40-100 mm long and conspicuously pubescent); follicles long-fusiform and pubescent; leaf abaxial surfaces densely gray-white pubescent; plants short shrubs (2-5+ dm tall); [s. TX only in our area]
                 9 Flowers white, pink or red, if salverform the floral tube primarily glabrous and much shorter in length (2-12 mm long); fruit a drupe (Ochrosia) or rounded to long-fusiform follicle (if long-fusiform, then not conspicuously pubescent); [collectively widespread non-natives, including s. TX, but naturalizing primarily in FL]
                   10 Plants lianas or subshrubs, often at least somewhat climbing; latex milky; leaves opposite, not whorled; stipular colleters interpetiolar and intrapetiolar; follicles strongly 3-angled, fusiform, and paired on the stem
                   10 Plants erect shrubs or trees; latex milky or clear; leaves usually whorled (sometimes opposite, or predominantly so in Tabernaemontana); stipular colleters interpetiolar only; fruit (follicles or drupes) terete or 2-angled, if paired then conspicuously elongate-cylindric (Alstonia; Nerium)
                     11 Ripened fruit bright red or orange and fleshy (the interior at least bearing a fleshy red or orange aril in Tabernaemontana); latex milky.
                       12 Leaf apex acuminate or apiculate; fruit a yellowish-orange follicle with seeds bearing orange-red arils
                     11 Fruit conspicuously elongate-cylindric, brown or red-brown follicles (not drupe-like nor fleshy); latex milky or clear.
                          13 Plants trees, 2-60 m tall, with a single or multiple stem(s); latex milky; flowers white or cream colored, the anthers not connivent and not adhering to stigmas; follicles [uncommon non-natives, s. FL]
                          13 Plants shrubs, 10-40 dm tall, much branched from the base; latex clear; flowers white, pink, or red, the anthers connivent and adhering to the stigmas; [commonly cultivated in our area (and sometimes persistent), particularly near the coast; NC s. to FL, w. to TX]
               8 Flowers yellow; plants erect subshrubs 4-12 dm tall (Angadenia berteroi) or trailing to erect woody vines 0-20 m tall (Allamanda); [native or non-native].
(c) portioid - CC-BY-SA
                            14 Leaves oblanceolate, 15-40 mm wide, mostly in whorls of 3-4; plants larger trailing or erect woody vines; follicles rounded and spiny; [non-natives of disturbed habitats, c. and s. FL].
                              15 Lateral veins of the leaf blades not or only slightly raised on lower surface; seeds winged; corolla tube (below stamen insertion) 2-4 cm long
                              15 Lateral veins of the leaf blades prominently raised on lower surface; seeds not winged; corolla tube (below stamen insertion) 1.0-1.8 cm long
                            14 Leaves narrowly elliptic to oblong, 2.5-10 mm wide, leaves opposite; plants smaller subshrubs; follicles smooth; [native of pine rocklands and marl prairies, s. FL]
  2 Plant an erect (or primarily upright) herb or trailing herbaceous vine (occasionally subshrubs in Cataranthus).
                                16 Flowers with conspicuous or less conspicuous corona; follicles not paired; seeds with coma present.
                                  17 Leaves alternate, or sometimes whorled (e.g., A. verticillata), variously shaped, but not both petiolate and cordate; plant either an erect herb or a decumbent herb with stiff, thick stems (> 4 mm in diameter)
                                  17 Leaves opposite, petiolate and cordate, 2-4 cm long; plant a trailing herbaceous vine with weak, thin stems (< 2 mm in diameter)
                                16 Flowers lacking corona; follicles paired (occasionally single by abortion); seeds with coma absent (Catharanthus, Amsonia) or present (Apocynum).
                                       19 Flower < 8 mm across; paired follicles pendent, 10-22 cm long; seeds with coma; mature plants normally > 7 dm tall; plants herbaceous
                                       19 Flower > 20 mm across; paired follicles erect, 1.5-2.5 cm long; seeds lacking coma; mature plants 2-6 dm tall; plants herbaceous or sometimes subshrubs
© Scott Ward
1 Plant twining (the stems wrapping around another plant), herbaceous or woody.
                                         20 Leaves conspicuously cordate at base (or subcordate to truncate in Vinceotoxicum), ovate to broadly lanceolate, ca. 1-4× as long as wide.
                                             22 Stem pubescence usually a mix of long eglandular and short, glandular-capitate hairs (the shorter hairs can be eglandular or glandular-capitate in Matelea); latex white; flowers variously colored: purple-black, maroon, brown, yellow, yellow-green, cream (white in Matelea baldwyniana); gynostegial corona < ½ as long as the corolla lobes.
                                               23 Corolla lobes glabrous on the outer surface; dorsal anther appendages laminar; follicles smooth and angled; leaves usually with a strong burnt popcorn or peanut butter smell when rubbed
                                               23 Corolla lobes glandular-puberulent or puberulent on the outer surface; dorsal anther appendages absent; follicles muricate (Matelea); leaves lacking a strong burnt popcorn or peanut butter smell when rubbed
                                             22 Stems glabrous, glabrate, or puberulent, if so lacking two distinct hair lengths and neither capitate-glandular (the puberulence either in conspicuous lines or of curved trichomes, often retrorse, and of similar length; latex white or clear; flowers primarily white or cream colored (except maroon in Vincetoxicum and occasionally reddish-maroon in Funastrum clausum); gynostegial corona > ¾ as long as the corolla lobes.
                                                 24 Corona with a conspicuous pentagonal ring present at the base of the staminal column (the structure apparent without dissection of flowers); latex white; stems glabrous or if pubescent, the trichomes curved (often retrorsely so)
                                                 24 Corona lacking a conspicuous pentagonal ring at the base of the staminal column; latex clear (except white in Cynanchum unifarium); stems glabrous to pubescent (if puberulent, often in lines).
                                                    25 Flowers primarily white (C. laeve) or cream-colored to yellowish or greenish-white (C. unifarium); corona a fleshy, lobed cup; stems puberulent in a single line (sometimes glabrate in C. unifarium); [natives, collectively widespread in our flora area]
                                                    25 Flowers light or dark maroon in color; corona not a fleshy cup, nearly as long as to longer than the corolla lobes; stem puberulence (including pedicels/peduncles) either distributed somewhat equally throughout stems or in decurrent lines from nodes; [non-natives, primarily northern and northeastern in our flora area]
                                                      26 Stem pubescence usually a mix of long eglandular and short, glandular-capitate hairs (the shorter hairs can be eglandular or glandular-capitate in Matelea); latex white; follicles muricate (studded) or smooth (sometimes ribbed, but lacking studs).
                                                        27 Follicles smooth, 5-angled but not conspicuously muricate; leaves usually with a strong burnt popcorn or peanut butter smell when rubbed
                                                        27 Follicles muricate (appearing studded); leaves lacking a strong burnt popcorn or peanut butter smell when rubbed
                                                      26 Stems glabrous, glabrate, or puberulent, if so lacking two distinct hair lengths and neither capitate-glandular (the puberulence either in conspicuous lines or of curved trichomes, often retrorse, and of similar length; latex white or clear.
(c) Horn, Jay
                                         20 Leaves not cordate at base (cuneate, rounded, or truncate; occasionally hastate or subcordate); leaves ovate, lanceolate, or linear, ca. 1.5-10x as long as wide.
(c) Bradley, Keith
                                                                   32 Flowers primarily white, whitish-green, creamy yellow, pure yellow, or light pink.
                                                                       34 Flowers with a gynostegial corona (crown-like structure), cream-white, greenish-white or pale pink colored (sometimes reddish-maroon in Funastrum crispum)
                                                                         35 Coronas in 1 whorl, lacking a pentagonal ring at the base of the staminal column (Leptadenia has an inconspicuous corona in 1 series that is ring-like, but the inner absent).
                                                                           36 Corolla lobes glabrous or if pubescent, not conspicuously so on the upper surfaces (usually confined to abaxial corolla lobe surfaces, if pubescent at all); latex white throughout; [native and non-natives, TX and FL]
                                                                              37 Corolla lobes 1.5-3.5 mm long (flowers smaller); leaves linear to ovate (but never hastate); plants with eglandular and minute glandular trichomes; [native of rocklands, woodlands, hammocks, pastures; TX and FL]
                                                                                38 Corolla lobes 8-25 mm long, rounded, spreading, white OR yellow; leaves coriaceous (except Pentalinon, which has membranous to subcoriaceous leaves); [native or non-native].