Chelone

Linnaeus

Sp. Pl. 2: 611. 1753. 1753

Common names: Turtlehead
Endemic
Etymology: Greek chelon, tortoise, alluding to fancied resemblance between flower back and tortoise back
Treatment appears in FNA Volume 17. Treatment on page 57. Mentioned on page 5, 12, 15, 59, 80, 81, 294.

Herbs, perennial; rhizomes producing 1–12 aerial stems. Stems erect, glabrous or glabrate. Leaves cauline, opposite; petiole present or absent; blade not fleshy, not leathery, margins serrate to dentate. Inflorescences axillary and terminal, spikelike cymes; bracts ovate to broadly lanceolate, margins ciliate or not. Pedicels absent or present; bracteoles ± as large as caly× lobes, nearly surrounding caly× of flowers they subtend. Flowers bisexual; sepals 5, proximally connate, caly× radially symmetric, campanulate, lobes ovate, outer lobes ± as wide as inner; corolla white, light pink-red, or dark purple throughout or white and pink to purple distally, bilaterally symmetric, bilabiate, tubular, tube base not spurred or gibbous, throat not densely pilose internally, lobes 5, abaxial 3, ovate to rounded with middle abaxial one elevated into villous to lanate, bearded palate nearly closing throat, adaxial 2; stamens 4(or 5), proximally adnate to corolla, didynamous, filaments pubescent to villous; staminode (0 or)1, spatulate; ovary 2-locular, placentation axile; stigma capitate. Fruits capsules, dehiscence septicidal. Seeds ca. 50, tan to light brown, darker towards center, globular to ovoid, wings present. x = 14.

Distribution

c, e North America.

Discussion

Species 4 (4 in the flora).

Chelone is a member of Cheloneae, which in North America includes Chionophila, Collinsia, Keckiella, Nothochelone, Penstemon, and Tonella. These genera share a cymose inflorescence, the presence of a staminode, simple hairs, and stems that contain pith (A. D. Wolfe et al. 2002). In phylogenetic analyses using molecular (Wolfe et al.) and morphological (A. D. Nelson 1995) data, species of Chelone occur in a clade with N. nemorosa. Chelone has a reduced cyme with relatively large bracteoles, adaxially ridged corollas, triangular pollen amb (grain shape from polar view), rugulate-reticulate pollen exine sculpting, and circumalate (surrounded by a wing) seeds; Nothochelone has a more-branched cyme with relatively small bracteoles, abaxially ridged corollas, circular pollen amb, reticulate pollen exine sculpting, and asymmetric seed wings (Nelson). Both genera have hypogynous disc nectaries (Wolfe et al.).

Species of Chelone occur in wetland habitats. Their seeds float readily and are likely dispersed by water. Flowers are pollinated by bumblebees (Bombus spp.; F. W. Pennell 1935). Some leaf and seed herbivores use species of Chelone as a host (N. E. Stamp 1984, 1987). Common examples of leaf herbivores include the Baltimore checkerspot (Euphydryas phaeton) on C. glabra as well as sawfly larvae (Macrophya nigra and Tenthredo grandis), which are known from C. glabra and C. obliqua. One common larval seed predator known from C. glabra and C. obliqua is an agromyzid dipteran (Phytomyza cheloniae).

Species and cultivars of Chelone are available from nurseries and florists. Plants can escape from cultivation (T. S. Cooperrider 1969) and may have become naturalized outside their native range, especially in New England. Chelone was used medicinally by Native Americans and pioneers (C. S. Rafinesque 1828[–1830]; D. E. Moerman 1998).

Purported examples of inter- and intraspecific hybridization in Chelone were reported by A. D. Nelson and W. J. Elisens (1999). Rare individuals of C. cuthbertii or C. lyonii with narrow leaf bases might be the result of hybridization with C. glabra or C. obliqua (Nelson 1995). Rare individuals of C. lyonii with pink-tipped staminodes might result from hybridization with C. cuthbertii (Nelson). Individuals of C. glabra with completely pink, red, or purple corollas might be the result of hybridization with sympatric species of Chelone that have similar corollas (Nelson); this seems to occur rarely based on morphologic and isozyme variation (Nelson and Elisens).

Chelone glabra and C. obliqua may be difficult to distinguish because all qualitative characters exhibit some overlap. Staminode colors usually are preserved in herbarium specimens; corolla and beard colors are often difficult to determine from dried plants.

Key

1 Petioles 0–3 mm; staminode apices purple; corollas pink-red to purple. Chelone cuthbertii
1 Petioles (0–)2–40 mm; staminode apices white to light pink or green, rarely purple; corollas completely dark pink, pink-red, red, or purple with abaxial surfaces sometimes paler to white, or completely white to white in tube and distally green-white, pink, red, or purple. > 2
2 Petioles (2–)10–40 mm; leaf blade bases rounded to truncate; bracts 2–7 mm; staminode apices white to light pink. Chelone lyonii
2 Petioles (0–)2–20 mm; leaf blade bases cuneate; bracts 4–23 mm; staminode apices white or green, rarely purple. > 3
3 Corollas completely white to white in tube and distally green-white, pink, red, or purple; palates white-bearded, rarely green-yellow-bearded; staminode apices green. Chelone glabra
3 Corollas dark pink to red to purple, sometimes paler to white abaxially; palates yellow-bearded, rarely white-bearded; staminode apices white, rarely green or purple. Chelone obliqua