Flora of North America species comparison

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Nemacaulis

cottonheads
Habit Herbs annual; taproot thin.
Stems

arising from the root, prostrate to spreading or erect, glabrous to glandular or lanate.
Leaves

persistent through anthesis, essentially basal, rosulate;

petiole indistinct;

blade linear to spatulate, margins entire.
Inflorescences

terminal, cymose;

branches mostly dichotomous, not brittle or disarticulating into segments, round, glabrous or sparsely lanate, sometimes glandular, secondary branches sometimes developing tardily;

bracts 3, connate basally, triangular to obovate, leaflike or scalelike, not awned, glabrous or glandular.
Peduncles

erect, slender, or absent.
Flowers

5–30 per involucre, sessile or pedicellate;

perianth white to rose, campanulate when open, narrowly urceolate when closed, glabrous or with gland-tipped hairs;

tepals 6, connate proximally, slightly dimorphic, entire;

stamens 3;

filaments basally adnate, glabrous;

anthers pink to red, oval.
Achenes

mostly included, brown to deep maroon or black, not winged, 3-gonous, glabrous.
Seeds

embryo curved.
Involucral

bracts obscure to obvious, in tight spiral, linear to lanceolate or narrowly ovate, not awn-tipped.

Nemacaulis
Distribution
from USDA
sw United States; nw Mexico
[BONAP county map]
Discussion

Species 1.

Nemacaulis is allied to Eriogonum subg. Ganysma and especially E. gossypinum. Like that species, N. denudata has flowers embedded in a dense mass of hairs, which is the only significant feature that the two have in common aside from being annuals, generally spreading in habit, and having rather densely pubescent stems and leaves. The flowers in Nemacaulis are arranged in glomerules, a feature unique in Eriogonoideae. The involucre is markedly different, being composed of several whorls of bracts, each of which subtends a flower. In this and all the other members of Eriogoneae, modification of the involucre appears to be a significant factor in the evolution of distinctive genera. In Nemacaulis, the entire glomerule is dispersed by on-shore breezes along the coast, an effective transport mechanism for the tiny seeds. Entire glomerules may be trapped in moist pockets of sand, thereby positioning several seeds in a favorable location. In the rapidly evolving derived annuals of Eriogonineae, any selective advantage is quickly adopted and survival enhanced in the rather harsh environment, where members of the subtribe abound.

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Source FNA vol. 5, p. 441. Author: James L. Reveal.
Parent taxa Polygonaceae > subfam. Eriogonoideae
Subordinate taxa
N. denudata
Synonyms Eriogonum section N.
Name authority Nuttall: Proc. Acad. Nat. Sci. Philadelphia 4: 18. (1848)
Web links 
Unless otherwise noted, all data comes from the online version of the Flora of North America, who have made most of their content available via a Creative Commons license (CC BY 4.0).



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