Flora of North America species comparison

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Macroptilium

bushbean
Habit Herbs or vines, biennial or perennial, unarmed; roots turnip-shaped or elongate.
Stems

twining, erect, semierect, or prostrate, slender, sometimes hollow, sparsely to densely pubescent.
Leaves

alternate, usually odd-pinnate, rarely unifoliolate;

stipules present, persistent, not prolonged proximally, veined;

petiolate;

leaflets 3, stipels persistent, often reflexed, blade margins entire or 2-lobed, surfaces pubescent or glabrescent.
Inflorescences

6–12-flowered, axillary, pseudoracemes, cleistogamous flowers present in some species, with modified inflorescences, tufts of bracts present at base of peduncle, persistent or caducous, nodes swollen, glandular;

node bracts present, caducous or inconspicuous, bracteoles present, usually caducous.
Pedicels

mostly shorter than calyx tube.
Flowers

papilionaceous;

calyx tubular or campanulate, lobes 5, lobes shorter to longer than tube, distinct or adaxial lobes partly connate;

petals connate;

corolla salmon-orange, red, or purple-black;

banner orbiculate, obovate, or oblong, emarginate;

wings ovate or oblong to obovate, conspicuously projected beyond distal bend of keel one directed upward to adopt function of banner;

keel incurved, beak hooked, tip of beak hidden by wings;

stamens 10, diadelphous;

anthers sub-basifixed;

ovary with nectary disc at base, style apically recurved and thickened, distal portion introrsely bearded, stigma terminal;

ovules 4–24.
Fruits

legumes, patent or pendent, substipitate, valves plane or twisting, linear or oblong-falcate, dehiscent, non-septate, pilose, strigose, or hirsute.
Seeds

2–20, oblong or reniform;

hilum not centric, oblong or ovate.
x

= 11.

Macroptilium
Distribution
from USDA
Mexico; Central America; South America; s United States; West Indies
[BONAP county map]
Discussion

Species 18 (4 in the flora).

Flowers of Macroptilium species often become purple when dry; in some species, the banner is mostly pale green, with two basal auricles, wings are larger than banner and long-stipitate, brightly colored, and glabrous or pubescent; keel petals are distally connate and hooklike and basally adnate to the staminal tube. Vexillary stamens are distinct and often dilated at base. The ovary is subsessile, pubescent, and surrounded at the base by a cylindric, nectariferous disc; the style has an introrse beard and is apically recurved and thickened, with a terminal stigma.

The greatest diversity in Macroptilium is found in South America (about 16 species; S. M. Espert et al. 2007); some species have been introduced for fodder and naturalized in the tropics and subtropics nearly worldwide.

Molecular evidence establishes the monophylly of Macroptilium among the other New World genera of Phaseolinae (A. Delgado-Salinas et al. 2011). A diagnostic feature is the flower architecture: one wing petal is directed upward to adopt the function of the banner petal, which becomes a supporting structure of the wing petal and encloses the distally-hooked keel characteristic of all of the species.

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Key
1. Stems twining or erect to semierect; taproots elongate; extrafloral nectaries conspicuous at inflorescence nodes; tufts of bracts at base of peduncle persistent; flowers 1.7–3 cm, corollas red or purple-black; legumes linear, patent, 7–10.5 cm, valves twisting at dehiscence; seeds 12–20.
→ 2
2. Stems twining, solid; leaflets papery, lateral blades 2-lobed, surfaces canescent abaxially, strigose adaxially; corollas purple-black; seeds 12 or 13; Arizona, California, Florida, Mississippi, New Mexico, Texas.
M. atropurpureum
2. Stems erect or semierect, hollow; leaflets membranous, lateral blades not lobed, surfaces strigulose abaxially, glabrescent adaxially; corollas red; seeds 15–20; Florida, Georgia, Louisiana, South Carolina.
M. lathyroides
1. Stems prostrate; roots turnip-shaped; extrafloral nectaries inconspicuous at inflorescences nodes; tufts of bracts at base of peduncle caducous; chasmogamous flowers 0.9–1 cm, corollas salmon-orange or red; legumes oblong-falcate, pendent, 1–2.5 cm, valves not twisting at dehiscence; seeds 2–5.
→ 3
3. Leaflet blades orbiculate, ovate to broadly ovate, or obovate, lateral blades sometimes 2-lobed; corollas salmon-orange; ovules 6; Arizona, New Mexico, Texas.
M. gibbosifolium
3. Leaflet blades linear, entire; corollas red; ovules 4; Arizona.
M. supinum
Source FNA vol. 11. Authors: Leticia Torres-Colín, Alfonso Delgado-Salinas.
Parent taxa Fabaceae > subfam. Faboideae
Subordinate taxa
M. atropurpureum, M. gibbosifolium, M. lathyroides, M. supinum
Synonyms Phaseolus section macroptilium
Name authority (Bentham) Urban: Symb. Antill. 9: 457. (1928)
Web links 
Unless otherwise noted, all data comes from the online version of the Flora of North America, who have made most of their content available via a Creative Commons license (CC BY 4.0).



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