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Isocoma acradenia var. eremophila   

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Isocoma acradenia var. eremophila
Isocoma acradenia var. eremophila
Photographer: Aaron Schusteff

ID: 0000 0000 0810 0214 (2010-08-04)

Copyright © 2010 Aaron Schusteff

  • date of photo  Jan 12, 2010
  • location   Off dirt road between Arroyo Salado Camp and 17 Palms Oasis, Anza-Borrego Desert State Park (San Diego County, California, US)
  • family Asteraceae
  • notes   Upper stem & inflorescence, showing toothed leaves and flower heads (with 10-13 florets per head here, counted using enlarged image).

    The species here is clearly Isocoma acradenia, but determining whether it is var. arcadenia or var. eremophila is problematic.

    The keys to varieties in The Jepson Manual and the Flora of North America refer principally to the leaf margins: mostly entire for variety acradenia vs. toothed for variety eremophila. Using this character, I'd say these plants were var. eremophila. The Jepson key also mentions leaf shape: ''narrowly oblanceolate'' for variety acradenia vs. ''narrowly obovate with long-tapering base to obovate'' for variety eremophila. While the plants here seem to fit the first case (var. acradenia) better, such leaf shape characters typically incorporate a lot of 'wiggle-room' and it could conceivably go either way with these plants.

    Referring to the Jepson Manual descriptions of var. acradenia and var. eremophila, the latter is generally larger (< 1.3 m) while the former is generally smaller (< 0.8 m). This would seem to point towards var. eremophila here...but, again, there's plenty of wiggle-room here so the distinction is not clear cut. The only other differing characters mentioned for these two varieties are: number of florets per head (6-12 vs. 7-14, resp.); and number of phyllaries ('22-28 in 3-4 series' vs. '< 28 in 3-5 series', resp.). The plants here had 8-13 florets per head, with 18-20 phyllaries in 3-4 series. Thus they'd tend towards var. eremophila, but given the overlap in these cases and natural variation, this is not a very satisfying discriminant. Moreover, the FNA descriptions state that var. acradenia has '18-24 florets per head' while var. eremophila has 12-20. These FNA numbers are inconsistent with Jepson, not only in magnitude, but also in indicating which taxon tends to have fewer-flowered heads. Moreover, neither of the FNA numbers fits the plants here. (Perhaps an error in FNA?) The (older) Munz flora describes 6-13 florets per head for var. acradenia vs. 15-25 for var. eremophila. So as far as number of florets go, the plants here would go to var. eremophila in Jepson and var. acradenia in Munz! The lack in consistency in these treatments makes me wonder about the clarity of distinction among these two subspecies.

    Finally, herbarium records for both subspecies exist in the general vicinity where these photos were taken. There is a 1985 herbarium record for var. acradenia very near the location of these photos, as well as herbarium records nearby for var. eremophila: one about 5.5 miles south from 2003, and another about 7 miles ENE from 2009. Presumably the 1985 record would have been ID'd using Munz, and if number of florets was given precedence the plants in my photos would have keyed to var. acradenia, perhaps explaining that discrepancy. In summary, overall it seems to me the best subspecies determinaton here is I. acradenia var. eremophila, though lacking certainty due to the various ambiguities discussed above.

  • photo category: Plant - annual/perennial

  • Look for Jepson Manual treatments, maps (University & Jepson Herbaria)
  • View Calflora record for Isocoma acradenia var. eremophila
  • View all photos in CalPhotos of Isocoma acradenia var. eremophila
  • Check Google Images for Isocoma acradenia var. eremophila

  • The photographer's identification Isocoma acradenia var. eremophila has not been reviewed. Click here to review or comment on the identification.

    Using this photo   The thumbnail photo (128x192 pixels) on this page may be freely used for personal or academic purposes without prior permission under the Fair Use provisions of US copyright law as long as the photo is clearly credited with © 2010 Aaron Schusteff. For other uses, or if you have questions, contact Aaron Schusteff arbonius2[AT] (Replace the [AT] with the @ symbol before sending an email.)


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