Slender twining woody vine; vegetative hairs medifixed; stipules borne on base of petiole; leaves usually bearing 2 small glands embedded in margin of lamina near its base (these occasionally apparently on petiole when lamina is decurrent), rarely eglandular. Inflorescence unbranched, mostly axillary to scars of leaves from previous seasons, leafless or bearing a pair of much-reduced, soon-deciduous leaves subtending lowest flowers; floriferous bracts eglandular or bearing 2 tiny marginal glands near base, persistent or eventually deciduous; pedicels sessile or short-pedunculate; bracteoles like bracts but smaller, one or both usually bearing (1) 2 small marginal glands near base. Sepals leaving outermost petal exposed in enlarging bud, bearing large paired abaxial glands, the glands10 but those of the anterior sepal connate with adjacent glands to form 2 larger compound glands; glands peltate, raised on stout stalks that elongate to 1–2 mm during anthesis, borne below free part of sepals; corolla bilaterally symmetrical, the posterior petal with a longer thicker claw and longer narrower limb than the lateral 4; petals abaxially densely appressed-tomentose on claw and limb and somewhat hairy adaxially on claw; lateral petals erose or dentate; androecium bilaterally symmetrical; stamens with the filaments diminishing in length from front to back, the anterior 3 longest and the posterior 3 shortest, abaxially thinly sericeous, connate at base; anthers glabrous; pollen with 4–6 vestigial colpi variously oriented and several pores, often at or toward opposite ends of adjacent colpi; gynoecium radially symmetrical, the carpels 3; styles 3, subequal (the anterior sometimes slightly shorter than the posterior 2), initially coherent but usually separating during anthesis, slender, the large distinct stigmas apical, elliptical-capitate and eccentric, dorsally elongated away from axis of flower. Fruit dry, breaking apart into 3 mericarps separating from a short pyramidal torus; mericarp covered on back and sides with many long, slender, vascularized setae arrayed in several roughly vertical rows but giving the impression of completely covering abaxial surface of nut; each seta plumose its whole length with short soft spreading white hairs. Chromosome number unknown.
In flower this woody vine is notable for its abaxially hairy yellow petals, the calyx glands raised on a thick stalk, and the initially coherent styles with terminal stigmas. Many specimens have the flowering or fruiting branches leafless but separate branches collected at the same time with leaves, suggesting that the plant produces flowers on older branches while it is producing leaves on new branches. In fruit this species is unlike anything else in the Caribbean, because instead of bearing three winged samaras like most malpighiaceous vines it produces three mericarps covered with many long vascularized setae. Each seta is softly hairy with short spreading white hairs (which are not obvious without a lens). The setae are not stiff spines; they probably act like wings and serve for dispersal by wind.
There are five neotropical genera that bear setiferous fruits, and Niedenzu (1928) put them all in a single tribe, Tricomarieae, but that tribe is not supported by molecular data (Davis et al., 2001, pdf), nor by other morphological characters (W. R. Anderson, personal observations). The only other genus in the Bunchosia clade with such fruits is the Mexican Echinopterys, which differs from Henleophytum in its eglandular sepals, mostly alternate leaves, hairy anthers, and ± permanently coherent styles. Given their similar fruits one would naturally expect Henleophytum and Echinopterys to be sister genera, but the molecular evidence currently available (C. C. Davis & W. R. Anderson, unpublished data) indicates that Henleophytum is sister to Heladena and Echinopterys is sister to Bunchosia and Thryallis. If that phylogeny is correct, it suggests that setose fruits evolved twice in this clade, but it is at least theoretically possible that the common ancestor of the clade had setiferous fruits, with the setae transformed into the winglets of Tristellateia and lost in Thryallis and Bunchosia.
See the discussion under Heladena for notes on the sister status of that genus and Henleophytum.
Etymology: Henlea was named in honor of J. Henle (1809–1885), professor of medicine at the University of Göttingen, where Grisebach was a professor. Henleophytum is simply the name Henlea with the addition of the Greek word for plant, phytum.
Photos: H. echinatum
Drawing: H. echinatum