Hemsleyna Kuntze, Rev. Gen. Pl. 1: 88. 1891.—Lectotype, designated by C. Anderson, 1995:
H. longifolia (Mart.) Kuntze [Thryallis longifolia Mart.].
Scandent shrubs and woody vines; vegetative hairs stellate; leaves bearing 1 or 2 pairs of glands at apex of petiole and/or on base of lamina. Inflorescences terminal and lateral, variously grouped; pedicels short-pedunculate or subsessile; floriferous bracts and bracteoles eglandular, persistent or deciduous. Sepals imbricated and completely concealing petals in enlarging bud, eglandular, reflexed to revolute in anthesis, elongating and becoming stiff and spreading in fruit; corolla bilaterally symmetrical, the posterior petal slightly smaller than the lateral petals; petals glabrous, the limb oblate (wider than long); lateral petals with the margin erose or irregularly dentate to nearly lacerate; androecium radially symmetrical; stamens glabrous, the filaments alike, proximally connate; anthers slightly longer opposite sepals than opposite petals; pollen with several poorly developed colpi or lacking ectoapertures and several randomly dispersed pores; gynoecium bilaterally symmetrical, the carpels (2) 3; styles as many as carpels, distinct, slender, the anterior style slightly longer than the posterior 2, the capitate stigmas apical but somewhat reflexed abaxially and briefly decurrent adaxially. Fruit dry, probably dispersed intact with the enlarged winglike sepals, tardily schizocarpic into (2) 3 small nutlets; nutlets rugose, with a prominent dorsal ridge or rudimentary winglet; developing seed embedded in spongy tissue (perisperm?), the mature seed completely filling the locule. Chromosome number: n = 29 (30) (W. R. Anderson, 1993a).
Five species of Brazil and adjacent Paraguay and Bolivia. These are mostly plants of open habitats (campo, cerrado, thickets, caatinga, restinga, secondary forest, roadsides), but they have occasionally been reported from gallery forest. [map]
Thryallis is one of the most easily recognized genera in the Malpighiaceae. All its hairs are stellate, a condition otherwise known only in a few species of Byrsonima. The hairs are unicellular, as always in the Malpighiaceae, but they have several radiating branches, not the two branches that typify the family. The eglandular imbricated sepals, concealing the petals in bud, are also distinctive, and the enlargement of the sepals in fruit, presumably as an aid to dispersal, while not without parallels in other genera, is certainly unusual. The oblate petal limbs give them a characteristic look, and the dry unwinged fruit, breaking apart belatedly into tiny nutlets, is unusual in the family.
Molecular data of C. C. Davis and W. R. Anderson place Thryallis as sister to Bunchosia with 95% bootstrap support. This result is surprising when one considers the most obvious morphological characters. Bunchosia differs from Thryallis in its arborescent habit, medifixed hairs, sepals leaving petals exposed in the bud, and fleshy indehiscent fruit; however, when one looks beyond those characters one finds some intriguing similarities and parallelisms. A few species of Bunchosia have spurs at the base of the hair stalks. The stipules are borne in the same position in the two genera, both genera have elongated pseudoracemes and glabrous lemon-yellow petals, and the stigmas in Thryallis are very similar to those in some species of Bunchosia, e.g., B. macilenta (see W. Anderson, 1987, p. 60). Lowrie (1982) noted that in some populations of Thryallis the pollen has lost its ectoapertures to become polyporate as in Bunchosia, and C. Anderson (1995) observed that in some populations of Thryallis the gynoecium is bicarpellate, as in at least half the species of Bunchosia.
In 1762 Linnaeus used the generic name Thryallis for the plant that we now know as Galphimia brasiliensis (L.) Adr. Juss. In 1829 Martius misapplied the name Thryallis to two Brazilian species of Malpighiaceae that are not at all closely related to the Thryallis of Linnaeus. Later students of Malpighiaceae, beginning with Adrien de Jussieu, used the name Thryallis for the genus of Martius and took up the name Galphimia Cavanilles (1799) for the plants assignable to Thryallis L. This practice was stabilized legislatively when the 1969 Botanical Congress conserved Thryallis Mart. against Thryallis L. Because of that action, Galphimia Cav. is the correct name for plants that would otherwise be called Thryallis L. Many people, especially in horticulture, persist in using the name Thryallis for Galphimia, but they are wrong to do so.
Etymology: Thryallis is a Greek word meaning "wick." According to Wittstein (1856) the name was used by pre-Linnaean botanists for a species of Verbascum with thick woolly leaves. Linnaeus (1762; pdf) gave no reason for applying that name to the plant that we call Galphimia brasiliensis (see discussion above), and Martius simply took up Linnaeus's name. It is true, as Wittstein pointed out, that both Verbascum and Galphimia (as well as Thryallis Mart.) have yellow flowers, but that seems unlikely to have anything to do with the meaning of the name.