Monographs Details: Hackelia diffusa var. arida (Piper) R.L.Carr
Authority: Gentry, Johnnie L. & Carr, Robert L. 1976. A revision of the genus Hackelia (Boraginaceae) in North America north of Mexico. Mem. New York Bot. Gard. 26: 121-227.
Description:Variety Description - Perennial, herbage light green or generally bluish-green throughout, 4-6 dm tall; stems generally several, erect, canescent, antrorsely strigose in the inflorescence, retrorsely strigose or often spreading, nearly tomentose below. Radical leaves generally few, less often many, 10-30 cm long, 4-11 mm wide, linear or narrowly elliptic, long-attenuate to a petiole of ca. 1/3 the total length, canescent-tomentose with rather straight trichomes, sometimes ap-pressed, very commonly of two size ranges; cauline leaves linear, sessile, usually less than 5 mm wide, the lowermost 8-14 cm long, those at midstem 5-8 cm long, becoming reduced upwards to minute bracts in the inflorescence. Pedicel 6-9(-17) mm in fruit. Calyx 2.5-3.5 mm long, linear-lanceolate. Corolla limb white, rarely cream, with a yellowish throat, 8-13(-18) mm wide. Fornices with appendages papillate-pilose, obscurely emarginate. Nutlets 3.3-4.0 mm long, narrowly oblong-ovate; dorsal surface evenly verrucose-hispidulous, the intramarginal prickles small but distinct, 8-16, rarely none; marginal prickles 1-2 mm long, connate for 1/3 (1/2) their length, often turning inward to form a somewhat cupulate border. Chromosome number, 2n = 48.

Discussion:Lappula arida Piper, Bull. Torrey Club 28: 44. 1901. Echinospermum aridum (Piper) K. Schum., Just’s Bot. Jahresber. 29(1): 564. 1903. Hackelia arida (Piper) Johnst., Contr. Gray Herb. 68: 48. 1923. Type. WASHINGTON. Ellensburg, May 1897, Piper 2676, (holotype, US!). Hackelia diffusa var arida morphologically and in habit most closely aligns with H. cinerea and H. ciliata; and upon further investigation it may be found that this rather highly variable taxon arose as a variant of H. ciliata. Regardless of its phylogeny, the origins of this taxon must have been in this area of central Washington, and from there it spread south where it encountered H. diffusa (var cottonii) in the Yakima region. It has since fully merged with the H. diffusa complex, and at present the transition between these two entities is so complete that their separation in the Yakima-Ellensberg region is impossible. A brief discussion of this relationship is found under H. diffusa var cottonii. There is a considerable amount of evidence which indicates that where this taxon encountered Hackelia venusta to the west there was an exchange of genetic material. Plants collected in the Lake Chelan area, Swakane Canyon, Navarre Coulee, Mitchell Creek, Lower Tumwater Canyon, as well as other areas, tend to have the following features: shorter papillae on the fornices; larger flowers and fornices; slightly larger nutlets with a broad flange often over one-half the length of the marginal prickles; broader basal leaves; and more persistent radical leaves than do other specimens of H. diffusa var arida. This interpretation runs contrary to the commonly held belief that typical H. cinerea is to be found in this area; i.e., the specimens with broad-flanged nutlets tend to have larger flowers and less pubescent fomices with large protuberances. These characters all diverge from H. cinerea but do indicate a strong possibility of introgression with H. venusta. There is a definite shape and size difference between the fomices of H. cinerea and H. diffusa var arida. The protuberances in H. diffusa var arida are almost always twice as long as the protuberances in typical H. cinerea. The shape of the protuberance in H. cinerea is typically deltoid whereas in H. diffusa var arida it is usually pandurate or nearly so. The following specimens have flowers considerably larger than are normally found in H. diffusa var arida: Lower end of Navarre Coulee, Ward 288 (WS, WTU, NY); hills around Lake Chelan, Fiker 1640 (WS); dry sagebrush slopes near Leavenworth, Thompson 8994 (DS, NY, UC, MO, GH, US); Alder Creek, near Twisp, Edwards 234 (WS, GH); Mitchell Creek grade, near Lake Chelan, Edwards 266 (GH). There are other collections, as well, but the above are indicative of the variation found in the corolla. The following specimens have nutlets with a broad, venusta-like flange, and quite commonly the nutlets also are larger than is typical of H. diffusa var arida: Eight miles up Swakane Canyon, Hitchcock 17338 (WS, RM, UC, ID); dry slopes along Swakane Canyon, Thompson 8530 (NY, GH); head of Swakane Canyon, Ingram 1930 (ORE); Thompson 8994 cited above; mountainside W of Leavenworth, Otis 674, (WS); Edwards 266, cited above; foot of Tronson Ridge, Thompson 9290 (DS, NY); Chelan Butte, Griffiths & Cotton 173 (WS, US). These specimens represent a sample of those with the nutlet characteristics discussed above. All the plants just cited are all similar to Hackelia diffusa var arida in habit but tend toward intermediacy with H. venusta in flower size and nutlets. The gene flow seems to have been from H. venusta to H. diffusa var arida because the three known populations of H. venusta appear to be stable, and to show little variation. We have not seen any plants that approach H. venusta in habit but show intermediacy toward H. diffusa var arida.
Distribution:United States of America North America|