Sp. Pl. 1: 3. 1753.
Gen. Pl. ed. 5, 4. 1754.
Herbs, annual or perennial, sometimes suffrutescent at base, slender, often glandular, glabrous, or pubescent, from slender and soft or stout, ± woody, and ropelike or fusiform taproot. Stems procumbent, decumbent, ascending, or erect, unarmed, with or without glutinous bands on internodes. Leaves petiolate, pairs unequal in size in each pair; blade thin or thick and slightly fleshy, base symmetric to asymmetric. Inflorescences terminal and axillary, pedunculate or not clearly pedunculate because of repeated branching from distal axils, diffuse, and then usually widely cymose, paniculate, or thyrsiform, terminal portions cymose, racemose, spicate, subumbellate, umbellate, subcapitate, or capitate, rarely borne singly; bracts ± persistent and not accrescent, or deciduous, 1–3 beneath each flower, distinct, lanceolate, minute, thin, translucent. Flowers bisexual, chasmogamous; perianth radially symmetric or slightly bilaterally symmetric, campanulate or widely funnelform, constricted beyond ovaries, tube abruptly expanded to (4–) 5-lobed limb; stamens 2–8, included or exserted; styles at or extending beyond anthers; stigmas peltate. Fruits fusiform, clavate, oblong-clavate, obovoid, or obpyramidal, stiffly coriaceous; ribs (3–) 5, rounded, angular, or winglike, smooth, glabrous or glandular-pubescent; sulci smooth or rugose, epidermal surface smooth, papillate, or minutely pubescent.
Warm-temperate and tropical regions worldwide
Species ca. 40 (16 in the flora).
Numerous authors, particularly those of the eighteenth and nineteenth centuries, “corrected” to Boerhaavia Linneaus’ intentional Latinization (Boerhavia) of Boerhaave’s name. Boerhavia sometimes includes Anulocaulis, Commicarpus, and Cyphomeris (F. R. Fosberg 1978). At the species level, there is variation that is often difficult to treat taxonomically, especially among annuals of the Sonoran Desert and the pantropical B. diffusa–B. coccinea complex. Many species probably are highly autogamous (R. Spellenberg 2000). P. C. Standley’s publications on the family in North America (1909, 1911, 1918) have been the basis for much of the subsequent floristic efforts, with all authors taking a more conservative approach. Nevertheless, careful examination of Boerhavia fruits indicates that some of the entities that Standley proposed represent distinct taxa. For most species in the flora, identification requires mature fruits. In this treatment, the range of ratios of length to width (l/w) of individual fruits of a species is given as a means to relate shape. Fruits from a number of Boerhavia species exude mucilage when wet (J. M. Willson and R. Spellenberg 1977).
|1||Fruits glandular-pubescent or minutely pubescent; plants perennial||> 2|
|1||Fruits glabrous (rarely with some minute pubescence in sulci); plants annual or perennial||> 4|
|2||Leaves mostly distributed throughout plant; inflorescences axillary or terminal; branches spreading-villous or hispid to minutely and finely pubescent; flowers usually more than 5 per cluster; fruits narrowly obovate and tapering at both ends or clavate, apex round or narrowly round-conic||Boerhavia coccinea|
|2||Leaves mostly concentrated in basal 1/2 of plant; inflorescences mostly terminal; branches glabrate or glabrous; flowers usually borne singly or up to 5 per cluster, occasionally more; fruits oblong-clavate or obpyramidal, apex round, broadly conic, or truncate||> 3|
|3||Perianths wine red or brick red, 2-4.5 mm; stamens well exserted; flowers usually borne singly on slender pedicels; fruits oblong-clavate, minutely pubescent, some- times with minute gland-tipped hairs||Boerhavia gracillima|
|3||Perianths purplish red to reddish pink or nearly white, 1-1.5 mm; stamens included or barely exserted; flowers usually in tight clusters of 2-5 at ends of branches; fruits obpyramidal, conspicuously stipitate-glandular||Boerhavia diffusa|
|4||Plants perennial; fruit ribs rounded or bluntly round-angled||> 5|
|4||Plants annual; fruit ribs obtusely to acutely angled, ribs sometimes winglike, rarely bluntly round-angled||> 8|
|5||Bracts at base of perianths soon deciduous after anthesis; perianths wine red to brick red; sulci of fruit usually smooth||Boerhavia gracillima|
|5||Bracts at base of perianths persistent; perianths red-pink, pink-lavender, pink, or white; sulci of fruit smooth or papillate||> 6|
|6||Leaves linear to lanceolate, rarely ovate; perianths 4-7 mm; stamens usually 5; surface of sulci smooth.||Boerhavia linearifolia|
|6||Leaves ovate to round; perianths 2.5-10 mm; stamens 3-8; surface of sulci minutely papillate||> 7|
|7||Perianths 5-10 mm; stamens (4-)5-8; edges of fruit ribs rounded, not overhanging sulci||Boerhavia anisophylla|
|7||Perianths 2.5-3 mm; stamens 3-5; edges of fruit ribs sharp, slightly over- hanging sulci||Boerhavia ciliata|
|8||Branches of inflorescence densely glandular-villous, rarely minutely pubescent or glabrous, without sticky bands on distal internodes; bracts at base of perianth 1.5-4 mm, ovate (occasionally lance-acuminate in B. wrightii), persistent; fruits 4- or 5-ribbed, ribs never winglike||> 9|
|8||Branches of inflorescence usually glabrous, sometimes minutely pubescent but not glandular, often with sticky bands on distal internodes; bracts at base of perianth 0.4-1.8 mm, usually lanceolate or narrower, deciduous; fruits (3-)5-ribbed, ribs sometimes winglike||> 10|
|9||Fruits 4(-5)-ribbed; inflorescences racemose or spicate, axis 10-35 mm||Boerhavia wrightii|
|9||Fruits 5-ribbed; inflorescences subcapitate or capitate, axis 0-2.5 mm||Boerhavia purpurascens|
|10||Terminal portions of inflorescences spicate or racemose||> 11|
|10||Terminal portions of inflorescences subracemose, subumbellate, umbellate, or capitate, or flowers borne singly||> 13|
|11||Fruits broadly obovoid (l/w: usually 1.7-2.1), usually overlapping in inflorescence; sulci and ribs slightly rugose; sulci usually about 0.5 times as wide as base of ribs; stems usually glandular and spreading-pilose basally||Boerhavia spicata|
|11||Fruits narrowly obovoid or obpyramidal (l/w: usually 2.1-3.1), overlapping in inflorescence or remote; sulci and ribs slightly rugose to smooth; sulci 0.1-1 times as wide as base of ribs; stems puberulent, often sparsely pilose, rarely glandular basally||> 12|
|12||Epidermal surface of sulci papillose; sulci 0.5-1 times as wide as base of ribs; sides of ribs strongly rugose||Boerhavia torreyana|
|12||Epidermal surface of sulci glabrous; sulci 0.1-0.3 times as wide as base of ribs; sides of ribs smooth or slightly rugose||Boerhavia coulteri|
|13||Fruits 3-4(-5)-ribbed, ribs acute or winglike||> 14|
|14||Inflorescences capitate clusters on short peduncles among leaves and terminal on branches; fruit tapering to stipelike base distal to pedicels||Boerhavia pterocarpa|
|14||Inflorescences repeatedly forked, ending in umbels or single flowers, usually well beyond leaves; fruit tapering to pedicels, without stipelike base||Boerhavia triquetra|
|13||Fruits (3-)-5-ribbed, ribs winglike or not||> 15|
|15||Sulci of fruits smooth or very slightly rugose; fruits with 5 winglike ribs||Boerhavia megaptera|
|15||Sulci of fruits slightly to prominently rugose; fruits with (4-)5 angular ribs||> 16|
|16||Terminal flower clusters usually precise umbels, all pedicels attaching at 1 node; occasionally terminal inflorescences 1-flowered; fruits 2-3.2 mm||Boerhavia intermedia|
|16||Terminal flower clusters irregularly umbellate or subracemose, at least some pedicels attaching well below others; terminal inflorescences rarely 1-flowered; fruits 2.7-4 mm||Boerhavia erecta|
"thin" is not a number.