Flora of North America species comparison

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Arabis pycnocarpa var. pycnocarpa

Arabis pycnocarpa var. adpressipilis
Photo is of parent taxon

blushing rock-cress, hairy fruit rock cress, hairy rockcress
Photo is of parent taxon
Stems

usually hirsute basally, rarely glabrescent, trichomes often simple, sometimes branched.

pilose, trichomes appressed, malpighiaceous, or minutely stalked, forked, plants rarely glabrescent.
Basal leaves

blade surfaces sparsely to densely pubescent, trichomes simple and stalked.

blade surfaces pubescent, trichomes sessile, forked, and/or stellate.
Fruits

(3.5–)4–5.8(–6) cm;

style (0.2–)0.5–1 mm, (rarely stout).

(4–)4.5–6(–6.5) cm;

style 0.5–1.3 mm.
2n

= 32.

Arabis pycnocarpa var. pycnocarpa

Arabis pycnocarpa var. adpressipilis
Phenology Flowering Mar–Jul. Flowering Mar–Jun.
Habitat Bluffs, cliffs, ledges, rocky hillsides, open woods, bottom lands, gravel bars, meadows, streamsides, upland prairies, grassy swales, hillsides, stream bottoms Ravines, pastures, cliffs, calcareous talus, dolomite glades, rich woods, bluffs, rocky ledges
Elevation 0-2500 m (0-8200 ft) 0-300 m (0-1000 ft)
Distribution
from FNA
AK; AZ; CA; CO; CT; IA; ID; KS; MA; ME; MI; MN; MT; ND; NE; NH; NJ; NM; NV; NY; OH; OR; PA; SD; UT; VA; VT; WI; WV; WY; AB; BC; LB; MB; NB; NS; NT; ON; QC; SK; YT; Asia (China, Japan, Russian Far East)
[BONAP county map]
from FNA
IA; IL; IN; KS; MO; NY; OH; PA; TN; VA; ON
[BONAP county map]
Discussion

Some populations in northern Indiana and northern Illinois, [e.g., Herman 8790 (Jo Davies County) and Friesner 19072 (Elkhart County), both at GH] most likely represent hybrids between the two varieties of Arabis pycnocarpa. Trichomes borne proximally on stems of these plants are a mixture of forked and simple. It is expected that hybrids can be found where the ranges of the two taxa overlap.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

R. C. Rollins (1941, 1993) recognized both pycnocarpa and adpressipilis as distinct varieties of Arabis hirsuta; G. A. Mulligan (1996) treated adpressipilis as a synonym of A. hirsuta var. pycnocarpa. In my opinion, the differences in trichome morphology of the stems and leaves are significant enough to justify recognition of infraspecific taxa of one species.

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Source FNA vol. 7, p. 260. FNA vol. 7, p. 260.
Parent taxa Brassicaceae > tribe Arabideae > Arabis > Arabis pycnocarpa Brassicaceae > tribe Arabideae > Arabis > Arabis pycnocarpa
Sibling taxa
A. pycnocarpa var. adpressipilis
A. pycnocarpa var. pycnocarpa
Synonyms A. hirsuta var. minshallii, A. pycnocarpa var. reducta A. hirsuta var. adpressipilis
Name authority unknown M. Hopkins: Rhodora 39: 117. (1937)
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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