Vines or herbs, perennial, herbaceous or woody at base; latex white. Stems decumbent, pros­trate, or ascending, twining or not, unarmed, vestiture a mix of short glandular and long eglan­dular trichomes. Leaves persistent or tardily deciduous, opposite, petiolate; stipular colleters interpetiolar, laminar colleters present. Inflorescences extra-axillary or terminal, umbelliform or racemiform, sessile, subsessile, or pedunculate. Flowers: calycine colleters present; corolla shades of green, red, purple, brown, white, or cream, rotate or campanulate, aestivation contort-dextrorse; corolline corona absent; androecium and gynoecium united into a gynostegium adnate to corolla tube; gynostegial corona whorls 1 or 2; anthers adnate to style, locules 2; pollen in each theca massed into a rigid, horizontally oriented pollinium, pollinia lacrimiform to reniform with abaxial excavation proximal to translator, joined from adjacent anthers by translators to a common corpusculum and together forming a pollinarium. Fruits follicles, typically solitary, commonly pendulous, sometimes lying on ground, green, brown or purple at maturity, sometimes gray-striate, terete, smooth or variously ornamented, glabrous or with various indumentum. Seeds ovate, flattened, winged, not beaked, comose, not arillate. x = 11.

Distribution

United States, Mexico, West Indies, Central America, South America.

Discussion

Species ca. 200 (22 in the flora).

R. E. Woodson Jr. (1941) adopted a broad (and polyphyletic) circumscription of Matelea, originally described as a genus of Amazonian shrubs, subsuming many small genera from North and Central America. To accommodate the diversity of an inflated Matelea, Woodson erected 16 subgenera. Subsequently, some distinctive elements have been removed (including Pherotrichis and Polystemma in the flora area), leaving Matelea in a state of temporary disarray until revision is complete. Dismemberment of Matelea is supported by a number of phylogenetic studies (S. Liede et al. 2005; A. Krings et al. 2008; A. McDonnell et al. 2018). In addition to difficulties in generic circumscription, Matelea in the flora area includes complexes with poorly understood species delimitation and a number of rare, local endemics that have been seldom collected and are poorly known. Among the Asclepiadoideae of the flora area, the species of Matelea are in greatest need of further taxonomic study.

The species in this treatment are ordered based on phylogenetic results (A. McDonnell et al. 2018). Within clades, species are often very difficult to distinguish, and in many cases it may be impossible to do so in the absence of flowering material. Some useful floral characters, such as color, the orientation of corolla lobes, and the form of the corona, are often distorted, obscured, or lost in herbarium material. Careful notes or photographs made at the time of collection are invaluable. Follicle morphology has not been sufficiently appreciated in differentiating species groups. Most species have muricate follicles, but in species 10–12, the follicles are typically tuberculate, whereas in species 7–9 they are typically smooth. Moreover, species 7–12 have follicles with conspicuously gray-striate coloration, similar to that of Polystemma, whereas the follicle color of the remaining species is more uniform. Leaf size is highly variable in most species. In this treatment, leaf measurements pertain only to leaves at nodes bearing inflorescences, at anthesis; thus, larger and smaller extremes are omitted from the ranges.

Selected References

None.

Lower Taxa

Matelea alabamensis, Matelea atrostellata, Matelea baldwyniana, Matelea biflora, Matelea brevicoronata, Matelea carolinensis, Matelea chihuahuensis, Matelea cynanchoides, Matelea decipiens, Matelea edwardsensis, Matelea flavidula, Matelea floridana, Matelea hirtelliflora, Matelea obliqua, Matelea parviflora, Matelea parvifolia, Matelea producta, Matelea pubiflora, Matelea radiata, Matelea reticulata, Matelea sagittifolia, Matelea texensis

Key

1	Stems not twining, plants decumbent, prostrate, ascending, or occasionally scandent on low vegetation (in M. pubiflora).	> 2
2	Corollas densely pilose to hirsute adaxially.	> 3
3	Corona with 2 whorls, an outer whorl of shorter, laminar segments and an inner whorl of longer, erect, subulate segments; inflorescences 2–20-flowered, pedunculate (peduncles 0.7–10 cm); s Texas.	Matelea parviflora
3	Corona with 1 whorl of united segments forming a ring, with adaxial, subulate, incurved appendages; inflorescences 1–6-flowered, sessile or subsessile; Florida, Georgia, New Mexico, Oklahoma, Texas (excluding s Texas).	> 4
4	Inflorescences 1–2-flowered; corollas rotate-campanulate, dark maroon or brown adaxially, lobes 3–6 mm; corona exposed; New Mexico, Oklahoma, Texas.	Matelea biflora
4	Inflorescences 1–6-flowered; corollas campanulate, green, yellow, or brown adaxially, lobes 2–3.5 mm; corona included within corolla; Florida, Georgia.	Matelea pubiflora
2	Corollas glabrous adaxially or inconspicuously hirtellous at base of lobes.	> 5
5	Corona segments overarching style apex, minutely hirtellous; corollas cream with green to pink lines that become reticulate towards lobe margins; bootheel of New Mexico.	Matelea chihuahuensis
5	Corona segments not overarching style apex, incumbent on backs of anthers or erect to spreading, glabrous; corollas green, yellow, brown, purple, or maroon, lined or not; Arkansas, Louisiana, Oklahoma, Texas.	> 6
6	Peduncles 0–3 cm; corolla lobes 2.5–4 mm, not reticulate; corona segment appendages incumbent on anthers and exceeded by style apex, green, yellow, or brown; follicles sparsely muricate (fewer than 1 protrusion per cm of length).	Matelea cynanchoides
6	Peduncles 0.7–10 cm; corolla lobes 1–2.5 mm, faintly to strongly reticulate; corona segment appendages not incumbent on anthers, exceeding style apex, white, greenish cream, green, or yellow; follicles moderately to densely muricate (more than 1 protrusion per cm length).	> 7
7	Inner corona segments erect to spreading, outer segments with minute to elongate marginal lobes at apex; corolla lobes spreading to reflexed; widespread in s Texas.	Matelea parviflora
7	Inner corona segments inflexed over style apex, outer segments unlobed at apex; corolla lobes ascending to spreading; local and rare in the vicinity of Laredo, Texas.	Matelea brevicoronata
1	Stems twining (at least at stem tips), usually climbing woody vegetation or fences, sometimes trailing and twining on herbs.	> 8
8	Leaf blades 0.5–2.5 × 0.2–1.3 cm; inflorescences sessile or subsessile; pedicels 1–5 mm; follicles tuberculate (protrusions blunt) to nearly smooth.	> 9
9	Corolla lobes 2–3 mm; leaf blades hirtellous adaxially; Arizona, California, trans-Pecos Texas.	Matelea parvifolia
9	Corolla lobes 5–10 mm; leaf blades sparsely puberulent to glabrate adaxially; s Texas, e of the Pecos River.	> 10
10	Corona segments 0.5–0.7 mm, exceeded by style apex, green, cream, or yellowish; corolla lobes linear; calyx lobes linear to linear-lanceolate.	Matelea sagittifolia
10	Corona segments 2.5–3 mm, greatly exceeding style apex, white with a purple adaxial patch; corolla lobes lanceolate; calyx lobes narrowly lanceolate.	Matelea radiata
8	Leaf blades 1.5–20 × 1–18 cm; inflorescences pedunculate, peduncles (0–)0.2–13 cm; pedicels 3–40 mm; follicles muricate (protrusions sharp) or smooth.	> 11
11	Corollas tubular-campanulate, green to reddish abaxially (rarely brown); coronas included in tube; vestiture of leaf blades wholly eglandular; Arizona, New Mexico, w Texas.	> 12
12	Corollas glabrous adaxially, tube 3.5–8 mm; widespread in Arizona, New Mexico, w Texas.	Matelea producta
12	Corollas hirtellous adaxially, tube 1.5–2.5 mm; local in Big Bend region, Texas.	Matelea texensis
11	Corollas rotate, rotate-campanulate, or campanulate; coronas not concealed in tube (corona sometimes concealed by erect corolla lobes in M. baldwyniana, M. carolinensis, M. decipiens, and M. obliqua, in which case the corolla is white or maroon to brown abaxially); vestiture of leaf blades a mixture of long eglandular and inconspicuous glandular trichomes (glandular trichomes lacking in M. edwardsensis); e United States to w Texas.	> 13
13	Leaf blades 2.5–5 × 1–3.5 cm, apex attenuate to long-acuminate; petioles 0.7–1.7 cm; peduncles 0–1 cm; inflorescences 1–5-flowered; coronas papillose; follicles smooth or with very sparse, low tubercules, prominently gray-striate; rare and local in Big Bend region of w Texas.	Matelea atrostellata
13	Leaf blades 1.5–20 × 1–18 cm, apex acute to acuminate; petioles 1–9.5 cm; peduncles 0.2–13 cm; inflorescences 1–40-flowered; coronas glabrous; follicles muricate, inconspicuously striate or uniform in color; e United States to w Texas.	> 14
14	Corollas green to yellow-green, strongly reticulate with dark green lines; coronas yellow or pale green (flowers rarely maroon in M. flavidula).	> 15
15	Corolla lobes with parallel, longitudinal lines, reticulate only towards margins, 3–4 mm, densely hirsute adaxially; corona segments free nearly to base; seeds 10–11 mm, chalazal end erose; stems sparsely and inconspicuously hirsute to glabrate; Edwards Plateau and surrounding area, Texas.	Matelea edwardsensis
15	Corolla lobes reticulate throughout, 4–11 mm, glabrous or hirtellous only at base of lobes adaxially; corona a low ring or with segments free only in upper one-half; seeds 7–10 mm, chalazal end entire (scarcely erose in M. alabamensis); stems densely hirsute; coastal plain of se United States to w Texas.	> 16
16	Coronas prominent, equaling or slightly exceeding style apex, segments free in upper one-half, with marginal lobes at apex; corolla lobes elliptic or oblong to oblanceolate; apical anther appendages truncate, covering less than 25% of style apex; rare and local from coastal plain of South Carolina s and e to Apalachicola watershed, Florida.	Matelea flavidula
16	Coronas a low, undulate or lobed ring, not reaching one-half the height of style, segments if present entire at apex; corolla lobes broadly ovate to nearly orbiculate; apical anther appendages deltoid or ovate, covering more than 50% of style apex; Apalachicola watershed in Florida and Georgia, w to Texas.	> 17
17	Peduncles 1–7 cm; pedicels 12–25 mm; corolla lobes 4–5 mm; inflorescences 3–10-flowered; follicles 8–15 cm, sparsely to moderately muricate; Texas.	Matelea reticulata
17	Peduncles 0.2–1.2 cm; pedicels 5–15 mm; corolla lobes 7–10 mm; inflorescences 1–5-flowered; follicles 4.9–8 cm, densely muricate; Gulf Coastal Plain in Alabama, Florida, Georgia.	Matelea alabamensis
14	Corollas shades of maroon, purple, brown, white, or cream (rarely green, yellow-green, pink, or orange), not or only faintly reticulate, coronas maroon, purple, white, or cream (rarely yellow, orange, or rose).	> 18
18	Corollas and coronas white to cream or yellow (rarely purple).	Matelea baldwyniana
18	Corollas and coronas shades of maroon, brown, or purple (rarely green, yellow-green, pink, rose, or orange).	> 19
19	Corolla lobes 3–7.5 mm.	> 20
20	Coronas equaling style apex, medial lobe of segments elongate, longer than lateral lobes; Florida, Georgia.	Matelea floridana
20	Coronas equaling or exceeding style apex, medial lobe of segments shorter than lateral lobes; Delaware to Georgia, w to Texas.	> 21
21	Corollas glabrous adaxially; coronas 2–3 mm diam.; Delaware to Georgia, w to Louisiana.	Matelea carolinensis
21	Corollas hirtellous adaxially (rarely glabrous); coronas 3–4 mm diam.; e Texas, sw Arkansas.	Matelea hirtelliflora
19	Corolla lobes 7–18 mm.	> 22
22	Corollas rotate to campanulate; coronas 2–3 mm diam.	Matelea carolinensis
22	Corollas rotate-campanulate to campanulate; coronas 3–5 mm diam.	> 23
23	Corollas pink, reddish, or maroon; coronas 5 mm diam., usually nearly round, seg­ments very fleshy; Cumberland Plateau, w slope of Appalachian Mountains, and surrounding areas, Pennsylvania to North Carolina, w to Mississippi River.	Matelea obliqua
23	Corollas purple to maroon; coronas 3–4 mm diam., usually pentagonal, segments laminar; Ozark Mountains and areas s and w, Missouri to Louisiana w to Kansas, Oklahoma, Texas.	Matelea decipiens