Euthamia

Perennials or subshrubs, 40–200 cm (rhizomes creeping, fibrous-rooted). Stems erect (nearly terete), simple or branched, glabrous or hairy. Leaves cauline; alternate; sessile; blades (± uniform along stems) linear to lanceolate (40–130 mm), margins entire, faces glabrous or hairy, sparsely to densely gland-dotted (dots obscure or evident, 0.1–0.25 mm diam., 0–86 per mm²). Heads radiate, borne singly or (glomerulate) in corymbiform or paniculiform arrays. Involucres obconic to hemispheric, (2.5–6.3 ×) 2.1–8.1 mm. Phyllaries 11–29 in 3–5 series, 1-nerved (flat), linear to ovate, bases often stramineous or pale, margins chartaceous or weakly cartilaginous, not scarious (apices with green zones, erose to ciliate), abaxial faces glabrous, little to very resinous. Receptacles flat, pitted (pit borders ± fimbrillate), epaleate. Ray florets 7–22(–35) (usually more numerous than disc florets), pistillate, fertile; corollas yellow. Disc florets 3–22, bisexual, fertile; corollas yellow, tubes shorter than tubular to slender-funnelform throats, lobes 5, erect to ascending, oblong-lanceolate; style-branch appendages lanceolate. Cypselae oblong to narrowly ellipsoid, ± terete, 2–4-nerved, strigose; pappi persistent, of 20–30, white, ± equal, antrorsely barbellate, apically attenuate bristles in 1 series. x = 9.

Distribution

North America, Mexico, introduced in Europe, Asia.

Discussion

Species 5 (5 in the flora).

Euthamia was formerly included in Solidago. Arrangements of heads, gland-dotted leaves, and DNA sequence data demonstrate that Euthamia should be treated as distinct from Solidago (L. C. Anderson and J. B. Creech 1975; R. D. Noyes and L. H. Rieseberg 1999).

Ambiguous and contradictory information has led to much debate about who named Euthamia (D. J. Sieren 1981; K. N. Gandhi 1999; G. L. Nesom 1999; J. L. Strother 2000). I consider correct authorship for this genus to be as given in Index Nominum Genericorum (http://ravenel.si.edu/botany/ing).

Euthamia is capable of tremendous phenotypic variation. Transitional aspects of a given plant are much more likely to be related to environmental factors than to introgression. Heights of arrays are determined by measuring from the summit of the plant to the bases of proximalmost head-bearing branches.

Selected References

Sieren, D. J. 1981. The taxonomy of the genus Euthamia. Rhodora 83: 551–579.

Lower Taxa

Euthamia caroliniana, Euthamia graminifolia, Euthamia gymnospermoides, Euthamia leptocephala, Euthamia occidentalis

Key

1	Stems glabrous and glaucous; arrays of heads not flat-topped, lengths of proximal branches 0.18–0.56 times array heights (creating multistoried aspects to arrays); apices of inner phyllaries acute to acuminate	Euthamia occidentalis
1	Stems glabrous or hairy, not glaucous; arrays of heads usually flat-topped or rounded, lengths of proximal branches 0.5–1 times array heights; apices of inner phyllaries obtuse to acute	> 2
2	Disc corollas 2.5–3.3(–3.4) mm; involucres 3–4.7(–5.3) mm	> 3
2	Disc corollas 3.3–4.8 mm; involucres (4–)4.5–6.3 mm	> 4
3	Stems glabrous or glabrate; leaf blades usually 1–3 mm wide (to 6 mm wide in some Maine and Nova Scotia populations), faces glabrous or glabrate, abundantly and prominently gland-dotted	Euthamia caroliniana
3	Stems glabrous or densely spreading-hirtellous; leaf blades usually 3–12 mm wide, faces glabrous or densely spreading-hirtellous, usually sparsely and obscurely gland-dotted	Euthamia graminifolia
4	Leaf blades linear to lanceolate, lengths 12–49 times widths, gradually reduced distally, faces abundantly and prominently gland-dotted, not pustulate; arrays (25–)35–60% of plant heights	Euthamia gymnospermoides
4	Leaf blades lanceolate to narrowly lanceolate, lengths 8–18 times widths, abruptly reduced distally, faces little and obscurely gland-dotted, sometimes pustulate;arrays 6–35% of plant heights	Euthamia leptocephala