IB. diffusa sensu Hawaiian botanists, pro parte, non L.; B. diffusa L. var. gymnocarpa Heimeri; B. d. var. pseudotetrandra Heimeri; B. d. var. pubescens (R. Br.) Choisy, pro parte; B. d. var. sandwicensis Heimeri;
mutabilis sensu auct., non R. Br.; B. tetrandra sensu auct., non G. Forster]
(ind) Alena, anena (Niihau), nena
Relatively robust perennial herbs with a thickened root and several prostrate stems radiating from the root crown, sparingly to many-branched. Leaves usually ovate to elliptic-ovate or suborbicular, 1-5 cm long, 5-5 cm wide, margins entire to gently sinuate, apex obtuse to acute, base rounded to truncate or subcordate, petioles 0.3-2 cm long. Flowers borne in axillary pedunculate cymes or pseudoumbels, usually from alternate axils, the peduncles appearing to be crowded aside from the axil proper by the growth of an axillary branch, which very soon bears axillary cymes, leaves often reduced gradually distally, creating a paniculate appearance, but with a clear central axis, peduncles branched only near tip, branching basically umbelliform, each branch ending in a glomerule of flowers, or the branch system reduced to a single umbelliform to glomerate cluster of flowers, or the peduncle bearing 1 pair of leaves and a glomerate cluster of flowers; perianth 2-2.5 mm long, strongly constricted below the middle, lower part glandular, 5-costate, limb pink or white, campanulate, shortly 5- lobed; stamens 2-4, subequal with perianth. Anthocarps clavate to ellipsoid, 3-4 mm long, apex rounded, 5-ribbed, very glandular to subglabrous or glabrous. [2n = 52*.] Extending from Africa eastward to eastern Polynesia and Hawaii, primarily coastal and usually at low elevations; in Hawaii occasional, probably formerly much more common, on shores and moderately dry coastal areas and leeward, at least semi-dry lower slopes, on Kure, Midway, and Pearl and Hermes atolls, Lisianski, Laysan, French Frigate Shoals, and all of the main islands.—Plate 139.
This is doubtless the most variable of all species of Boerhavia, and certainly the most polymorphic in Hawaii. Some of the Hawaiian plants approach B. glabrata, while others approach the central Pacific B. albiflora Fosb. Some also come close to B. tetrandra, but none appear to be true B. tetrandra.
Several species and a number of varieties have been segregated more or less clearly from Boerhavia repens, but more must be described to portray the full range and localization of its variability. Variety repens is African and may include some Indian Ocean island plants. Heimeri (1937) included it in Boerhavia diffusa and described several Hawaiian varieties that certainly belong here. Without more critical study of the types, however, they can not be satisfactorily associated with definite Hawaiian populations and are not transferred here. After B. glabrata and B. herbstii are removed, the remaining indigenous Hawaiian plants may be sorted into about 9 varieties, some of them certainly extending to other Pacific island groups. Much careful field study will be required to determine whether these represent discrete population series or are merely nodal points of a heterogeneous variation pattern. The likelihood that the usually glandular fruits adhere to seabirds and shorebirds makes isolation of subpopulations only a temporary phenomenon, at best. In view of this, the greater part of the Hawaiian Boerhavia plants are here included in Boerhavia repens sensu lato.