Hexastylis Raf. (Aristolochiaceae)

With eleven species represented in the state, North Carolina is the epicenter of Hexastylis diversity. Only Hexastylis naniflora is listed at the federal level (Fed T, S3 G3). Hexastylis contracta is state listed (State E, S1 G3). Hexastylis rhombiformis and H. rosei are also of conservation concern and tracked by NHP.

Federally listed taxon—Hexastylis naniflora (Fed T, State T | S3 G3)

Habitat. Like most Hexastylis species, H. naniflora can be found on acidic soils. It is usually associated with hardwood bluffs and slopes adjacent to creeks or other bodies of water.

Range. Endemic to North and South Carolina.

Note. USFWS is proposing delisting this species. The public comment period ended 25 June 2021.

Additional resources. NHP | Recovery Plan | 5-yr review | Proposed delisting

Key to Hexastylis in North Carolina

Key adapted from Blomquist (1957), Gaddy (1987), Whittemore and Gaddy (1997 [FNA]), and Weakley (2008). Photos by Krings, unless otherwise indicated. Maps courtesy of USDA PLANTS and the North Carolina Natural Heritage Program.

1. Style extension distinctly bifid to stigma; leaves triangular to ovate-sagittate or subhastate, variagation (if present) between secondary veins...H. arifolia

1’. Style extension notched or divided at the apex, but not bifid to the stigma; leaves cordate, subreniform, orbicular, or triangular-cordate, variagation (if present) along secondary veins...2.

2. Leaf margins minutely toothed...H. rosei

2'. Leaf margins entire...3.

3. Inner surface of calyx lobes pilose, many trichomes whitish or translucent at least in part; leaves not clumped, spread out along long-creeping rhizomes...H. lewisii

3’. Inner surface of calyx lobes puberulent, trichomes usually purplish or reddish throughout; leaves usually strongly clumped...4.

4. Calyx tube broadly urceolate-campanulate or rhombic-ovate...5.

5. Calyx tube urceolate-campanulate, lobes 10–22 mm wide at base...H. shuttleworthii var. shuttleworthii

5’. Calyx tube rhombic-ovate (broadest near the middle), lobes 3–8 mm wide at base...6.

6. Internal calyx tube reticulations absent or poorly developed, ridges < 1.0 mm if present; ovary ca. 1/3 inferior ...H. contracta

6’. Internal calyx tube reticulations well developed, ridges 1.5–2 mm tall; ovary superior...H. rhombiformis

4’. Calyx tube cylindrical to narrowly cylindro-urceolate...7.

7. Calyx tube cylindrical to narrowly cylindro-urceolate, lobes 2–4 mm long, erect to slightly spreading...H. virginica

7’. Calyx tube cylindrical, lobes 4–15 mm long, moderately spreading to reflexed...8.

8. Calyx tube usually wider than long, orifice wider than the lobe lengths (lobes 9–16 x 8–16 mm); ovary ca. 1/3 inferior...9.

9. Calyx tube 12–25 mm long, leaves always densely variegated...H. minor

9'. Calyx tube 8–18 mm long, leaves sparsely variegated to not variegated...H. sorriei

8’. Calyx tube at least as long as wide or longer, orifice narrower than the lobe lengths; ovary superior or
half-inferior...10.

10. Calyx tube 7–14 mm wide, lobes 6–17 mm wide; ovary superior; leaves typically not variegated
...H. heterophylla

10’. Calyx tube 4–7 mm wide, lobes 4–7 mm wide; ovary half-inferior; leaves typically variegated...H. naniflora*

Similar species

Leaves of Asarum canadense s.l. may at first glance be taken for Hexastylis. However, note the distinct differences in flower structure in the images below. In contrast to Hexastylis, the flowers of Asarum canadense s.l. are conspicuously pubescent and the perianth lobes are not completely fused into a tube.

Asarum canadense
Leaf of Asarum canadense s.l. (Photo: Krings)
Asarum canadense
Flower of Asarum canadense s.l. (Photo: Krings)
Asarum canadense
Flower of Asarum canadense s.l. (Photo: Krings)
Asarum canadense
Flower of Asarum canadense s.l. (Photo: Krings)
Asarum canadense
Flower of Asarum canadense s.l. (Photo: Krings)
Asarum canadense
Flower of Asarum canadense s.l. (Photo: Krings)
Asarum canadense
Flower of Asarum canadense s.l. (Photo: Krings)