Sp. Pl. 1: 342. 1753.
Gen. Pl. ed. 5, 159. 1754.
Herbs, perennial, subscapose, glabrous, from stout rhizomes; roots contractile, fibrous. Stems erect, simple, hollow, glabrous. Leaves evergreen, in basal rosettes, reduced distally to bractlike leaves; blade simple, oblong-spatulate to oblanceolate, margins entire, apex acute, glabrous. Inflorescences terminal, racemose, dense, ebracteate, pedicellate. Flowers spreading, fragrant, funnel-shaped; tepals persistent, 6, distinct to barely connate basally, purplish pink, becoming green, spatulate to oblong, nectary proximal, adaxial, weakly sulcate; stamens persistent, 6, equaling tepals; filaments distinct, inner 3 proximally adnate to ovary; anthers dorsifixed, versatile, 1-locular, extrorse, pollen sacs apically confluent; ovary superior, 3-locular proximally, 1-locular distally; septal nectaries absent; styles 3, depressed apically into ovary apex, ascending to arching, distinct, sessile; stigmas not papillate along adaxial surface. Fruits capsular, deeply 3-lobed, papery, dehiscence loculicidal. Seeds 16 per locule, linear-fusiform, caudate at both ends. x = 17.
e North America.
The close relationships among Helonias and the east Asian Heloniopsis A. Gray and Ypsilandra Franchet have been noted repeatedly. They exhibit many similarities in morphology and anatomy (F. Buxbaum 1925, 1927; W. Schulze 1978b; C. Sterling 1980; F. H. Utech 1978b; F. H. Utech and S. Kawano 1981; N. Tanaka 1997, 1997b, 1997c, 1997d, 1997e, 1998), palynology (M. Takahashi and S. Kawano 1989), ecology (S. Kawano and J. Masuda 1980; H. Takahashi 1988), and karyology (F. H. Utech 1980). Based on these similarities, Tanaka merged the five species of Heloniopsis and the three species of Ypsilandra into Helonias. However, molecular evidence indicates that, although the genera are related, they are distinct (S. Fuse and M. N. Tamura 2000). This group has been recognized as a separate tribe, Heloniadeae Fries, within the Melanthiaceae sensu stricto (M. N. Tamura 1998; W. B. Zomlefer 1997b), or placed in a separate family, Heloniadaceae J. Agardh (A. L. Takhtajan 1997).
Helonias in eastern North America and the Ypsilandra–Heloniopsis lineage in eastern Asia comprise a paired Arcto-Tertiary element in which Ypsilandra (western China to the Himalayas) and Heloniopis (Taiwan, Korea to Japan) have differentiated from each other in eastern Asia (N. Tanaka 1997e).