Chaptalia texana Seedlings, 26 May 2010 — Achenes from April

Chaptalia Reproduction: Chasmogamy, Cleistogamy? & Apomixis?
by Bob Harms  email-here

Reproduction of our two Chaptalia species remains a mystery.

Context: The sole pollen source for sexual reproduction is from the small set of central florets.

Possibilities that have been discussed in conjunction with Chaptalia:

Evidence for Early Spring Phase Chasmogamy

With both species in early spring (March—early April) clumps of pollen are pushed up from the central florets and pollen can be seen on the style branches of the pistillate florets.
(Place curson on image for date.)
BCk-hd4-9Apr_1541-4in.jpg bkfnc-hd3-9Apr-hdtop-4in.jpg

Although I did not observe any pollinators during this period, I did not determine whether the pollen on a given head was from another plant. Self–pollination must be considered as a possibility.

March and early April C. texana heads aborted and dried.

Spring 2010

Rain during the Chaptalia texana peak bloom period in March—April 2010 may have prevented pollination. The earliest (March — early April) open–heads of C. texana did not produce mature/viable achenes, as shown above. But later, in mid April, numerous heads did mature to produce viable achenes. In late April 2010 C. texana again ceased to produce viable achenes, perhaps due to rising temperatures and rapidly drying soil. On April 23 only 5 buds were found; none of these produced mature heads, although one continued to develop through May 15.

C. texana achenes collected in mid April were collected and planted in a container. The rate of germination was quite high. (Photo at top of this page)

C. carduacea head (visible ligule type) with well-developed achenes, April 27. [click to enlarge]

C. carduacea head (reduced ligule type) with well-developed achenes, April 8. [click to enlarge]

C. carduacea blooms somewhat later, and perhaps also because of its closed heads, did not seem impacted by weather conditions in 2010. Aborted heads were not noted and well developed achenes at dispersal were the rule. However, inspection of C. carduacea achenes (April 8) image above shows that not all achenes were equally well developed. Those in the center that are less well developed, enlarged below with red lines, belong to perfect central florets (visible within the surrounding pappus wall). Cleistogamy can thus be ruled out, since it would benefit only the central perfect florets.

Although the central florets do develop apparently well–formed achenes, a relatively large number of them do not. A set of 24 central–floret achenes collected at dispersal gave the following results: 8 (below left) were clearly well developed; 7 (marked with green 'x') were smaller, but possibly ok; 9 (red 'x') did not seem to have developed.


This was not typical for the eligulate pistillate florets, only a few of which had aborted.

I conclude that in spring 2010 during the early spring phase pollen from the central florets was essential for fertilization for both species. Self–pollination cannot be ruled out. No support for cleistogamy or apomixis was found.

Self–pollination in Spring 2011

In spring 2011, during a period of extreme drought, both species produced fertile achenes during their peak blooming periods. Individual plants of both species in cultivation in my yard, isolated from conspecific populations in both distance and bloom period,* produced fully developed achenes. I consider this to be strong evidence of self–pollination.

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