Flora of North America species comparison

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Pterostegia

pterostegia, woodland threadstem
Habit Herbs, annual; taproot slender.
Stems

arising directly from the root, sprawling and spreading, solid, not fistulose or disarticulating into ringlike segments, thinly pubescent.
Leaves

persistent, cauline, opposite;

petiole present;

blade broadly elliptic to fan-shaped, margins entire or lobed.
Inflorescences

terminal, cymose, uniparous due to suppression of secondaries distally;

branches dichotomous, not brittle or disarticulating into segments, round, thinly pubescent;

bracts absent.
Peduncles

absent.
Flowers

2–3 per involucral cluster;

perianth pale yellow to pink or rose, campanulate when open, urceolate when closed, sparsely pubescent abaxially;

tepals (5–)6, connate for ca. 1/3 their length, monomorphic, entire apically;

stamens 6;

filaments adnate to perianth, glabrous;

anthers yellow, oval.
Achenes

included, yellowish brown to brown, winged, globose, glabrous.
Seeds

embryo straight.
Involucral

bracts 1, erect, 2-winged, reticulately veined, lobed or notched, slightly gibbous with age, invaginated adaxial surface hyaline.
x

= 14.

Pterostegia
Distribution
from USDA
w United States; nw Mexico
[BONAP county map]
Discussion

Species 1.

Pterostegia and the Baja California, Mexico, endemic Harfordia are the only genera of the tribe Pterostegieae. In both, the involucre is highly modified, becoming a slightly to markedly gibbous, reticulated, winged structure that encloses the mature achene. In Pterostegia, the two wings are slightly enlarged, but in Harfordia the wings are greatly inflated, which apparently aids in achene dispersal.

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Source FNA vol. 5, p. 477. Author: James L. Reveal.
Parent taxa Polygonaceae > subfam. Eriogonoideae
Subordinate taxa
P. drymarioides
Name authority Fischer & C. A. Meyer: Index Seminum (St. Petersburg) 2: 48. (1836)
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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