Hexastylis

Herbs, perennial, evergreen, rhizomatous, without aerial stems. Leaves alternate, 2-ranked; stipules absent; petiolate foliage leaves and sessile, triangular scale-leaves both present. Leaf blade membranous or leathery, glabrous. Inflorescences terminal on rhizome, solitary flowers, subtended by triangular bract. Flowers: sepals connate for most of length, usually mixture of brown, purple, or yellow, externally glabrous, inner surface glabrous, with weak to strong network of ridges, calyx tube never forming differentiated utricle or syrinx; vestigial petals absent; stamens 12, distinct; filaments shorter than pollen sacs; terminal appendage of anther absent or rudimentary; ovary superior or partly inferior, 6-locular; styles 6, distinct (except sometimes at extreme base). Capsule fleshy, dehiscence irregular. Seeds ovoid, not winged, with fleshy appendage. x = 13.

Distribution

North America.

Discussion

Species 10 (all in the flora).

Hexastylis is very similar to the Asiatic genera Heterotropa C. Morren & Decaisne and Asiasarum F. Maekawa; a strong case could be made for combining the three genera. Nevertheless, all three of these genera seem distinct from Asarum (in which they have been included by some authors; e.g., K. Barringer 1993) in their connate sepals, distinct styles, nonappendiculate anthers, and superior or partly inferior ovaries.

Herbarium specimens of Hexastylis are difficult to work with. The form of the calyx is very important taxonomically, but the calyx is fleshy and brittle and does not press well. Allowing flowers to wilt for several hours before pressing may help to reduce distortion, because the calyx becomes more flexible and less likely to split in the press. Features of the inner surface of the calyx are also important, but collectors seldom cut open flowers and press them with the inside visible. For this reason, herbarium specimens of Hexastylis are difficult to identify reliably, and meaningful work on the group requires field studies. L. L. Gaddy (1987) and H. L. Blomquist (1957) gave photographs and drawings of flowers of all species, and an extensive collection of liquid-preserved flowers is housed to the University of Tennessee; these are very helpful in identifying Hexastylis specimens.

Selected References

Blomquist, H. L. 1957. A revision of Hexastylis of North America. Brittonia 8: 255-281.

Gaddy, L. L. 1987. A review of the taxonomy and biogeography of Hexastylis (Aristolochiaceae). Castanea 52: 186-196.

Lower Taxa

Hexastylis arifolia, Hexastylis contracta, Hexastylis lewisii, Hexastylis minor, Hexastylis naniflora, Hexastylis rhombiformis, Hexastylis shuttleworthii, Hexastylis speciosa, Hexastylis virginica

Key

1	Sterile tip of style deeply 2-cleft, sinus reaching stigma; leaf blade triangular to ovate-sagittate or subhastate.	> 2
1	Sterile tip of style undivided or shallowly 2-cleft, sinus not reaching stigma; leaf blade cordate to orbiculate, triangular-cordate, or subreniform.	> 3
2	Calyx not abruptly contracted near middle, urceolate-campanulate or ovoid, tube smooth internally, lobes erect or spreading.	Hexastylis arifolia
2	Calyx abruptly contracted near middle, proximally narrowly cup-shaped, distally broadly cylindric, tube reticulately ridged internally, lobes spreading.	Hexastylis speciosa
3	Inner surface of calyx lobes pilose; rhizomes dimorphic, internodes of flowering rhizomes short, leaves crowded at rhizome apex, internodes of sterile rhizomes often long, leaves scattered along length of rhizome.	Hexastylis lewisii
3	Inner surface of calyx lobes puberulent; rhizomes not dimorphic, internodes short, leaves crowded at rhizome apex.	> 4
4	Calyx tube broadly urceolate-campanulate or rhombic-ovoid, conspicuously tapered above middle.	> 5
4	Calyx tube cylindric to narrowly cylindric-urceolate, not much tapered above middle.	> 7
5	Calyx tube urceolate-campanulate; calyx lobes 10–22 mm wide.	Hexastylis shuttleworthii
5	Calyx tube rhombic-ovoid; calyx lobes 3–8 mm wide.	> 6
6	Internal reticulations of calyx tube well developed, ridges 1.5–2 mm high; ovary superior.	Hexastylis rhombiformis
6	Internal reticulations of calyx tube absent or poorly developed, ridges 0–1 mm high; ovary ca. 1/3-inferior.	Hexastylis contracta
7	Calyx lobes erect or weakly spreading, 2–4 mm; calyx tube cylindric to narrowly cylindric-urceolate.	Hexastylis virginica
7	Calyx lobes moderately spreading to reflexed, 4–15 mm; calyx tube cylindric.	> 8
8	Calyx tube wider than long, its opening wider than length of lobes.	Hexastylis minor
8	Calyx tube at least as long as wide, its opening narrower than length of lobes.	> 9
9	Calyx tube 4–7 mm wide, lobes 4–7 mm wide.	Hexastylis naniflora
9	Calyx tube 7–14 mm wide, lobes 6–17 mm wide.	Hexastylis heterophylla