Apocynaceae

Trees, shrubs, lianas, vines, or herbs, perennial, taprooted, rhizomatous, or tuberous; latex milky (clear). Stems prostrate, trailing, erect, climbing, or twining, indument absent or variously of unicellular or multicellular glandular or eglandular trichomes. Leaves deciduous, semipersistent, or persistent, cauline, alternate, opposite, or whorled; stipules absent, stipular colleters variously basal to petiole, interpetiolar, intrapetiolar, or absent; petiole present or absent; blade margins entire, venation pinnate, pinnipalmate, or a single vein, laminar colleters borne at adaxial base or absent. Inflorescences extra-axillary, axillary, terminal, or pseudoterminal, cymose, often racemiform, umbelliform, corymbiform, or paniculiform, pedunculate (sessile). Flowers: perianth and androecium hypogynous [perigynous, epigynous]; sepals 5, connate, calycine colleters absent or present; petals 5, connate, corolla rotate, rotate-reflexed, campanulate, funnelform, urceolate, tubular, or salverform, aestivation dextrorse, sinistrorse, or valvate; corolline corona absent, annular, or of 5 scales or pads; stamens 5, antisepalous, epipetalous, sometimes connate throughout; anthers 2-thecous, free, connivent, or adnate to gynoecium and forming a gynostegium, margins with corneous wing in species with a gynostegium, 2- or 4-locular; gynostegial corona absent or of 5 separate or united scales, filaments, cups, or other diverse forms; pollen in monads, tetrads, or massed in each theca into a rigid pollinium, translators absent or present, when present, receiving tetrads of adjacent anthers (Cryptostegia) or joining pollinia of adjacent anthers to a common corpusculum, together forming a pollinarium; pistils 1, 2-carpellate, connate only by style apices; ovaries superior [partly inferior], 1-locular; styles 1 or 2, apical; stigmas subapical or lateral; ovules few–numerous; nectaries variously around the base of ovaries, on gynostegium, on receptacle, or absent. Fruits follicles, capsules, berries, or drupes, solitary or paired, erect or pendulous, striate, spiny, winged, or smooth. Seeds few–numerous, brown or black, flattened, navicular, or cylindric, marginally winged or not, comose or not, arillate or not.

Distribution

nearly worldwide, especially in tropics and subtropics.

Discussion

Genera ca. 460, species ca. 4800 (36 genera, 175 species in the flora).

From the early nineteenth into the latter half of the twentieth centuries, the pollinia- and gynostegium-bearing species were segregated as the family Asclepiadaceae Borkhausen. The structure of the combined androecium and gynoecium and their function in pollination are the most complex among eudicots (P. K. Endress 1994). Ample morphological and molecular phylogenetic evidence provided a sound basis for reuniting these families (M. E. Fallen 1986; H.-E. Wanntorp 1988; B. Sennblad and B. Bremer 1996). As yet, the sister group of Apocynaceae within Gentianales is uncertain, with some analyses indicating Gelsemiaceae and others Gentianaceae (P. F. Stevens 2001 onwards, http://www.mobot.org/MOBOT/research/APweb/). The current classification of Apocynaceae allocates genera to five subfamilies and further into tribes and, in some cases, subtribes (M. E. Endress et al. 2014). Three subfamilies that composed the former Asclepiadaceae (Asclepiadoideae Burnett, Periplocoideae R. Brown ex Endlicher, Secamonoideae Endlicher) have been repeatedly demonstrated to be monophyletic, whereas both of the remaining two subfamilies that composed Apocynaceae in the narrow sense (Apocynoideae Burnett, Rauvolfioideae Kosteletzky) are clearly paraphyletic (T. Livshultz et al. 2007). We follow the current classification here, recognizing that future revisions will be required to obtain monophyletic higher taxa. Genera of Rauvolfioideae (nos. 1–13), Apocynoideae (nos. 14–23), Periplocoideae (no. 24), and Asclepiadoideae (nos. 25–36) are present in the flora area.

Apocynaceae species possess diverse secondary compounds, some of which are potent toxins or are pharmacologically active. The indole alkaloids vincristine and vinblastine present in Catharanthus roseus are used in the treatment of Hodgkin’s lymphoma, leukemias, and other cancers. Toxic cardiac glycosides in Asclepias are sequestered by several species of milkweed-feeding insects for use in their own defense, most famously by the monarch butterfly (S. B. Malcolm 1991). Species of Vinca have long been cultivated as evergreen ground covers with showy flowers; species of Amsonia and Asclepias are also widely cultivated, especially for the nectar-rich flowers that are attractive to butterflies and other insects. Cultivated Vinca and Vincetoxicum species readily naturalize, are considered invasive, and present serious manage­ment concerns.

The following species have been reported as naturalized or escaped from cultivation, but are excluded from this treatment because convincing proof of persisting populations is lacking: Calotropis gigantea (Linnaeus) W. T. Aiton, C. procera (Aiton) W. T. Aiton, Gomphocarpus fruticosus (Linnaeus) W. T. Aiton, G. physocarpus E. Meyer, Metaplexis japonica (Thunberg) Makino, Periploca graeca Linnaeus, and Vincetoxicum hirundinaria Medikus.

Calotropis gigantea and C. procera are infrequently cultivated in California and Florida. Two collections of C. procera are known outside of cultivation. In California, the species was collected in an agricultural area in Imperial Valley (Laemmlen s.n., UCR-51373). The single individual was destroyed with no subsequent sign of naturalization in the area (A. C. Sanders, pers. comm.). In Florida, collections have been made from a soil dump (suspected to be from the Bahamas) in Hillsborough County in which numerous exotic species appeared (A. R. Franck, pers. comm.; Dickman s.n., USF-273524).

Gomphocarpus fruticosus [Asclepias fruticosa Linnaeus] and, especially, G. physocarpus [A. physocarpa (E. Meyer) Schlechter] have been cultivated in the flora region; the popularity of G. physocarpus appears to have increased dramatically in recent years because of its rapid growth and the novelty of the inflated, soft-spined follicles. Neither species is winter hardy in most of our region, although they may persist for a few years as far north as USDA Plant Hardiness Zone 7. Nonetheless, these species have not been documented often by herbarium specimens from the region, and in nearly all cases it is certain that they represent cultivated plants. A recent collection of G. physocarpus made in Ventura County, California, in 2016 (Provance 1116-02, UCR-278890) may represent the beginning of an established population. Botanists in California, Florida, and Texas should be cognizant of the possibility that these species may establish here, as they have in subtropical regions around the world.

Metaplexis japonica [Cynanchum rostellatum (Turcz.) Liede & Khanum] was reported from an Iowa State University agricultural research farm in the late 1950s and early 1960s (S. L. Welsh and D. E. Anderson 1962). It was suggested that the species may have been introduced during World War II through investigations of fiber sources. Eradication measures were undertaken, and there is no evidence from collections—or observations (D. A. Lewis, pers. comm.)—that the species persists in the state. An additional collection of the species was made in Canyon County, Idaho, in 1966 (Linford s.n., ID-106861). However, no additional collections have been made since, and western botanists report being unaware of any populations of the species in the state at this time (B. Ertter, pers. comm.; J. Smith, pers. comm.).

Until the end of the last century, Periploca graeca was cultivated as an ornamental subject across the warmer parts of the flora region. It seems to have fallen out of favor in recent times. There are several collections housed at herbaria, all of which pertain to cultivated plants or plants persisting for years to perhaps decades around homesteads. However, P. graeca does not appear to be naturalized anywhere in our region.

Vincetoxicum hirundinaria [synonyms: Cynanchum medium (Decaisne) K. Schumann, not R. Brown, C. vincetoxicum (Linnaeus) Persoon, V. medium Decaisne, V. officinale Moench] has been rarely cultivated in the region but is widely reported as a member of regional floras. Reports of naturalized populations ascribed to V. hirundinaria (or one of its synonyms) pertain to V. rossicum.

Selected References

None.

Lower Taxa

Allamanda, Alstonia, Amsonia, Angadenia, Apocynum, Araujia, Asclepias, Carissa, Catharanthus, Cryptostegia, Cycladenia, Cynanchum, Echites, Funastrum, Gonolobus, Haplophyton, Mandevilla, Matelea, Metastelma, Nerium, Ochrosia, Orthosia, Pattalias, Pentalinon, Pherotrichis, Plumeria, Polystemma, Rauvolfia, Rhabdadenia, Tabernaemontana, Thevetia, Thyrsanthella, Trachelospermum, Vallesia, Vinca, Vincetoxicum

Illustrations

Apocynaceae Illustrations

Key

1	Coronas gynostegial, at least in part; androecium fused with gynoecium into a gynostegium; pollen massed into rigid pollinia [Asclepiadoideae].	> 2
2	Stems not twining.	> 3
3	Leaves alternate or whorled.	Asclepias
3	Leaves opposite or subopposite.	> 4
4	Follicles broadly ovoid, muricate throughout with sparse, thick protuberances, too heavy for stems to support and lying on ground; stems prostrate to ascending; herbage clothed in a mixed indument of long, eglandular and minute, glandular trichomes.	Matelea
4	Follicles narrowly to broadly fusiform or lance-ovoid, not muricate throughout (if muricate throughout, follicles erect, aerial); stems prostrate to erect or vining; herbage glabrous or with various indumentum, but not glandular (if glandular in part [Pherotrichis], follicles aerial and sharply deflexed).	> 5
5	Follicles sharply deflexed; stems and leaves densely hirsute with long eglandular and minute glandular trichomes; corollas urceolate, cream with longitudinal green lines.	Pherotrichis
5	Follicles erect, spreading, or pendulous; stems and leaves glabrous or with various indumentum, trichomes never glandular; corollas rotate or campanulate, variously colored, but never cream with longitudinal lines.	> 6
6	Inflorescences umbellate, extra-axillary; corollas variously colored; follicles usually erect (if pendulous, coronas white, cream, ochroleucous, or rarely red-violet in part, sometimes tinged pink, green, or yellow, or with red-violet line).	Asclepias
6	Inflorescences cymes, axillary; coronas pinkish tan, reddish, or dark purple; follicles pendulous.	Vincetoxicum
2	Stems twining, at least at tips.	> 7
7	Leaf bases cuneate to rounded (subcordate), blades linear.	> 8
8	Coronas double, consisting of a pentagonal ring at base of staminal column and 5 discrete, vesicular segments at base of anthers; corolla lobes 3+ mm.	Funastrum
8	Coronas absent or single, consisting of 5 discrete or basally united, laminar segments arising from staminal column; corolla lobes to 4 mm.	> 9
9	Coronas absent; corollas yellow, becoming orange with age, tubular with incurved lobes.	Funastrum
9	Coronas single, consisting of 5 discrete or basally united, laminar segments arising from staminal column; corollas cream, yellow, or green, not becoming orange with age, campanulate, lobes not incurved.	> 10
10	Inflorescences axillary, sessile; corona segments united at base; corolla lobes glabrous adaxially; leaves caducous and stems often leafless.	Orthosia
10	Inflorescences extra-axillary, pedunculate (if sessile, corolla lobes densely puberulent or villous); corona segments discrete or united; corolla lobes glabrous, puberulent, or villous adaxially; leaves persistent.	> 11
11	Corolla lobes puberulent to villous adaxially; leaf blades chartaceous; corona segments discrete; aestivation valvate.	Metastelma
11	Corolla lobes glabrous adaxially; leaf blades fleshy; corona segments united at base; aestivation contort-dextrorse.	Pattalias
7	Leaf bases truncate to cordate, blades lanceolate to ovate or orbiculate.	> 12
12	Stems and/or leaves with a mixed indument of minute glandular hairs and longer eglandular hairs (if glandular hairs obscure, follicles with winged angles and dorsal anther appendages present); follicles 5-angled, muricate or tuberculate (if smooth, then gray striate and apex acuminate or long-attenuate).	> 13
13	Anthers with laminar dorsal appendages; follicles angled.	Gonolobus
13	Dorsal anther appendages lacking; follicles not angled, surfaces muricate, tuberculate, or smooth.	> 14
14	Follicles smooth, muricate, or tuberculate, sometimes gray striate; glan­dular trichomes not accumulating white crystals in dried specimens; style apex concave, planar, or convex, not bifid.	Matelea
14	Follicles smooth, mottled green and gray; glandular trichomes accumulating white crystals in dried specimens; style apex beaked, bifid.	Polystemma
12	Stems and leaves puberulent to glabrous, eglandular; follicles lacking angles and protuberances, not mottled.	> 15
15	Latex clear; inflorescences axillary or extra-axillary (if extra-axillary, corona segments deeply bifid).	> 16
16	Corollas and coronas cream; inflorescences extra-axillary; coronas of 5 separate, laminar, deeply bifid segments; follicles 2.5+ cm wide.	Cynanchum
16	Corollas and coronas pale reddish brown to dark purple; inflorescences axillary; coronas thick, 5-lobed rings or 5 thick, entire segments; follicles to 1 cm wide.	Vincetoxicum
15	Latex white; inflorescences extra-axillary (corona segments entire or 3-lobed).	> 17
17	Corolla lobes 1.5–3.5 mm; coronas 1 whorl of 5 discrete, laminar segments 1–2.5 mm; follicles 0.3–0.7 cm wide.	Metastelma
17	Corolla lobes 3–13 mm; coronas 1 or 2 whorls of discrete or basally united segments or a ring, if segments discrete and laminar, then 2.5–6 mm; follicles 0.3–7 cm wide.	> 18
18	Coronas 2 whorls, a pentagonal ring at base of staminal column and 5 discrete, vesicular segments at base of anthers; follicles 0.3–1.6 cm wide.	Funastrum
18	Coronas 1 whorl of 5 discrete or basally united, laminar segments or a tube longer than and obscuring gynostegium; follicles 1.5–7 cm wide.	> 19
19	Corollas pubescent abaxially; coronas a tube or 5 discrete, oblong or quadrate segments; seeds 5–7 × 1.5–3 mm.	Araujia
19	Corollas glabrous abaxially; coronas of 5 basally united, laminar segments; seeds 6–10 × 4–6 mm.	Cynanchum
1	Coronas absent or corolline only; stamens distinct, anthers connivent or not, but androe­cium not fused with gynoecium into a gynostegium; pollen free, sometimes in tetrads [Apocynoideae, Periplocoideae, Rauvolfioideae].	> 20
20	Pollen shed onto translators; follicles fusiform, strongly 3-sided.	Cryptostegia
20	Translators absent; fruits various, if follicles, then terete or somewhat compressed in cross section, not 3-sided.	> 21
21	Stems climbing, twining, trailing, or sprawling (sometimes suberect in Pentalinon and Rhabdadenia).	> 22
22	Corollas yellow.	> 23
23	Leaves usually whorled, sometimes opposite; aestivation sinistrorse; cap­sules solitary, spiny.	Allamanda
23	Leaves opposite; aestivation dextrorse; follicles paired, glabrous or pubes­cent, but not spiny.	> 24
24	Corollas to 10 mm, lobes 3–4 mm, spreading to strongly reflexed; follicles 10–23 mm.	Thyrsanthella
24	Corollas 15+ mm, lobes 7–25 mm, spreading to ascending; follicles 60+ mm.	> 25
25	Petioles 1–2 mm; abaxial leaf surface glabrous; calyx lobes broadly ovate, 1–2.5 mm, glabrous; corolla lobes 7–13 mm; anther connectives not appendiculate; follicles 60–90 mm.	Angadenia
25	Petioles 5–12 mm; abaxial leaf surface pubescent; calyx lobes linear-lanceolate, 7–12 mm, pubescent or glabrate; corolla lobes 20–25 mm; anther connectives appendiculate, elongate appendages intertwined; follicles 120–180 mm.	Pentalinon
22	Corollas white, pinkish white, pale yellow, cream, or shades of blue or purple.	> 26
26	Aestivation sinistrorse; corollas blue-purple, blue-violet, violet, or reddish purple (rarely white or pale blue).	Vinca
26	Aestivation dextrorse; corollas white, pinkish white, pale yellow or cream.	> 27
27	Corollas to 10 mm, lobes 2–5 mm wide.	> 28
28	Leaves deciduous; corolla lobes 3–4 × 2–3 mm, spreading to reflexed.	Thyrsanthella
28	Leaves persistent; corolla lobes 7–10 × 4–5 mm, spreading.	Trachelospermum
27	Corollas 15+ mm, lobes 6+ mm wide.	> 29
29	Corollas salverform, adjacent corolla lobes not overlapping or for at most ¼ length from the base.	Echites
29	Corollas funnelform, adjacent corolla lobes overlapping for ½+ of their length from the base.	> 30
30	Petioles 1–2 mm; calyx lobes 1–2.5 mm; seeds 4–8 mm.	Angadenia
30	Petioles 5–15 mm; calyx lobes 5–12 mm; seeds 10–30 mm.	> 31
31	Peduncles 20–40 mm, sparsely pubescent; calycine colleters present; seeds very narrowly oblong, 10–12 mm.	Pentalinon
31	Peduncles 75–100 mm, glabrous; calycine colleters absent; seeds linear, 25–30 mm.	Rhabdadenia
21	Stems erect or ascending (slightly spreading in Catharanthus and Cycladenia).	> 32
32	Stems armed with paired spines.	Carissa
32	Stems unarmed.	> 33
33	Leaves whorled (sometimes opposite at lower nodes; subverticillate keys in alternate lead).	> 34
34	Aestivation sinistrorse; shrubs; corollas white, lobes ± as long as wide; fruits fleshy, initially red, maturing black.	Rauvolfia
34	Aestivation dextrorse; combination of characters otherwise.	> 35
35	Latex milky; calycine colleters absent; corollas salverform, lobes 3–7 mm; corolline coro­nas absent; anthers not connivent, not adherent to stigma; nectaries annular.	Alstonia
35	Latex clear; calycine colleters present; corollas funnelform, lobes 15–25 mm; corolline coronas lacerate; anthers connivent, adherent to stigma; nectaries absent.	Nerium
33	Leaves alternate or opposite (subverticillate in Amsonia and Mandevilla).	> 36
36	Aestivation dextrorse.	> 37
37	Herbaceous perennials; calycine colleters absent.	> 38
38	Stems 20+ cm; latex milky; stipular colleters interpetiolar; corolla lobes to 3 mm; corolline coronas of 5 small, sagittate squamellae; pollen in persistent tetrads.	Apocynum
38	Stems 6–12 cm; latex not milky; stipular colleters absent; corolla lobes 4+ mm; corolline coronas absent; pollen free.	Cycladenia
37	Subshrubs, shrubs, or trees; calycine colleters present (absent in Ochrosia).	> 39
39	Latex clear; corolline coronas lacerate; nectaries absent.	Nerium
39	Latex milky; corolline coronas absent; nectaries 2–5 or annular.	> 40
40	Leaves deciduous, laminar colleters present; stipular colleters interpetiolar; Arizona, New Mexico, Texas.	Mandevilla
40	Leaves persistent, laminar colleters absent; stipular colleters absent or intrapetiolar; Florida.	> 41
41	Stipular colleters intrapetiolar; corollas white or cream, nec­taries annular; fruits drupaceous, red, ellipsoid to ovoid.	Ochrosia
41	Stipular colleters absent; corollas yellow to very pale yellow, nectaries 5, alternating with stamens; fruits follicles, green, terete to slightly moniliform.	Angadenia
36	Aestivation sinistrorse.	> 42
42	Leaves opposite.	> 43
43	Stipular colleters absent; corollas blue-purple, blue-violet, violet, or reddish purple (rarely white or pale blue).	Vinca
43	Stipular colleters intrapetiolar or both intra- and interpetiolar; corollas white, cream, pink, red, magenta, red-violet, or yellow.	> 44
44	Leaf surfaces, peduncles, and calyces pubescent; corollas yellow.	Haplophyton
44	Leaf surfaces, peduncles, and calyces glabrous (sometimes sparsely pubes­cent in Catharanthus roseus and ciliate in Tabernaemontana divaricata); corollas white, cream, pink, red, magenta, or red-violet (sometimes yellow in Tabernaemontana alba).	> 45
45	Subshrubs or herbs, 3–10(–20) dm; corollas white, pink, red, magenta, or red-violet, tube (15–)20–30 mm, throat 4–5 mm, lobes broadly obovate, often mucronulate; follicles erect; seeds not arillate.	Catharanthus
45	Shrubs or trees, 5–30(–150) dm; corollas white or cream (some­times yellow in Tabernaemontana alba), tube 3–12 mm, throat 3–15 mm, lobes obliquely elliptic, obovate, or dolabri­form; follicles deflexed; seeds arillate.	Tabernaemontana
42	Leaves alternate (to subverticillate in Amsonia).	> 46
46	Herbaceous perennials or shrubs/subshrubs to 60 cm.	> 47
47	Inflorescences terminal, thyrsoid or corymbose cymes; corollas blue to purplish or lavender (infrequently white or pink); seeds not comose.	Amsonia
47	Inflorescences axillary, solitary or occasionally 2-flowered; corollas yellow; seeds with comas on both ends.	Haplophyton
46	Trees or shrubs 1+ m.	> 48
48	Corollas yellow or orange; fruits green to black, dehiscent drupes.	Thevetia
48	Corollas white; fruits brown follicles or white, indehiscent drupes.	> 49
49	Corolla tubes 9–20 mm, lobes (15–)25–35(–45) × 10–15 mm; stamens inserted near base of corolla tube; follicles brown; leaves deciduous.	Plumeria
49	Corolla tubes 6–7 mm, lobes 3–5 × 1.2–1.6 mm; stamens inserted at or near orifice of corolla tube; drupes white; leaves persistent.	Vallesia