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Nova Scotia west to ND, south to FL and TX.
Similar to Arisaema triphyllum but with the following differences: spathe strongly fluted (i.e. with pale, broad and raised longitudinal veins); spathe flange 1-3 mm wide (vs. 2-9 mm wide); margins of the spathe tube often forming a V-shaped opening at the summit (vs. contiguous as the summit); distal portion of the spadix more or less cylindrical (vs. more or less club-shaped); underside of leaves green (vs. glaucous); typically flowering a few weeks later in the spring.
Flowers late May to June in central NY.
Wetland Indicator: NA
Most current authors treat this taxon as a subspecies of A. triphyllum. One reason sometimes given for this is that it is difficult to distinguish them in herbarium specimens but in the field this species is quite distinct. Another is that putative hybrid plants exist, though strict genetic isolation is not a usual requirement for the recognition of a plant species. Some of the presumed hybrids found have been either triploid or diploid and of unknown fertility. The fact that A. stewardsonii blooms later in the year suggests some degree of reproductive isolation.
Typical A. triphyllum is tetraploid while A. stewardsonii is diploid. Another diploid taxon, A. pusillum (A. triphyllum ssp. pusillum) is more common southward and resembles a diminutive A. triphyllum. It may be more likely for A. pusillum and A. stewardsonii to hybridize since they have the same chromosome number.
Arisaema stewardsonii is found almost exclusively in sphagnum swamps in central NY and is absent from upland situations.
Gleason, Henry A.
and A. Cronquist. 1991. Manual of Vascular Plants of Northeastern United States
and Adjacent Canada. Second Ed.
The New York Botanical Garden. Bronx, NY
Huttleston, D. G. 1949. The three subspecies of Arisaema triphyllum. Bulletin of the Torrey Botanical Club, 76(6): 407-413.
Thompson, S. A. 2000. Arisaema triphyllum in Flora of North America. Vol. 22. Accessed 22, April, 2015. http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=222000013
© Michael Hough 2018