Chaptalia texana & C. carduacea Phyllaries
by Bob Harms  email-here

Phyllaries provide the most striking evidence distinguishing these two species. Although we find considerable overlap in length of the longest (innermost) phyllaries (C. carduacea 15–20 mm long (avg. 17.7 mm) vs. C. texana 12.3–17.5 mm long (avg. 15 mm), the two are otherwise quite distinct. The exposed margins and midribs of C. carduacea phyllaries are dark crimson and stand in sharp contrast with the light tomentose vestiture in between, as can be seen in the images below. Specimens of C. texana with similar coloration were noted, but the absence of this contrast would seem to exclude C. carduacea.

The main distinguishing features are:

C. carduacea C. texana
subulate & subulate–linear linear lanceolate
stiff by virtue of a thick midrib which continues to the tip
    (ca. 0.23 mm thick 3 mm from the tip)		 tips acute and flexible
    (ca. 0.1 mm 3 mm from the tip)
innermost phyllaries 15–20 mm long (avg. 17.7 mm),
    of two widths, ± 1.1 mm & ± 1.8 mm		 innermost phyllaries 12.3–17.5 mm long (avg. 15 mm),
    of uniform width, ± 1 mm
outer phyllaries commonly greater than 1.5 mm wide outer phyllaries not exceeding 1.5 mm
clearly imbricate subimbricate
  1. subulate vs. linear lanceolate
    Click for larger image
    C. carduacea C. texana

  2. stiff vs. flexible

    Note that the ligules of C. texana essentially force the phyllaries to reflex — where there are no ligules, the phyllaries don't bend. With C. carduacea the ligules manage to reflex a bit only between the stiff phyllaries.
    Click for larger image
    C. carduacea C. texana

    Cross sections of longest phyllary tips at 1 mm, 2 mm and 3 mm (top to bottom) show the relative thickness of the phyllary apex midribs. (Scale is the same for images made at 45x magnification.)
    Click for larger image
    C. carduacea C. texana
    Perhaps also a consequence of phyllary stiffness/flexibility is the difference in involucre form. With C. texana the involucre is often subconical, narrowing from base to top, especially in fruit (by 40—50%). Although some narrowing with C. carduacea was noted, it was never so strong.

    And C. texana heads are frequently twisted:

  3. inner phyllary width
    Click for larger image

    C. carduacea (left) — C. texana
    The innermost phyllaries are easily viewed after achene dispersal, when the phyllaries and receptacle remain at the top of the peduncle (and with specimens pressed in that state).

  4. outer phyllary width
    Click for larger image
    C. carduacea C. texana

  5. imbricate vs. subimbricate
    Click for larger image

    C. carduacea (left) — C. texana
    Both species have ca. 6 series of phyllaries, but only with C. carduacea (left) do these have regularly arranged, overlapping edges. The phyllaries of C. texana are much more randomly distributed in relation to adjacent series. (The random arrangement makes it difficult to isolate the phyllaries. Note that each phyllary of C. texana has only one broad green midrib.)

Type specimen phyllaries

The distinctly different phyllaries of C. carduacea were one of the few characteristics given by E. L. Greene in asserting its status as a new species (1906):
“bracts subulate and subulate-linear, hard and rigid, pungently acute, tomentose”
Greene's C. leonina (presented in the same 1906 article) is regarded here as synonymous with C. carduacea (earlier both were seen as synonymous with C. texana). He says:
“bracts of the involucre broad and much imbricated, tomentose except as to the purple margins and tips, the latter pungently acute ... in aspect more like the Texan C. carduacea than any other.”
The images below were scanned from type specimens of the U. S. Herbarium.
Click for larger image

C. texana, G. C. Neally 297 US
October 1890, Western Texas

C. carduacea, M. B. Croft s.n. US
1884-1888, San Diego, Texas
C. leonina Greene, E. Palmer 766 US
Ferbruary to October 1880. Coahuila & Nuevo Leon, Mexico

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