Chaptalia texana Bud to Dispersal Development over 3 Weeks
by Bob Harms  email-here

In the hope of better understanding the development of head/peduncle opening/closing & nodding behavior, single buds that had not yet opened were marked and changes were noted (and at times photographed) at 2–4 day intervals until an achene dispersal stage had been reached (a process that took roughly 3 weeks).

Open–head plants

On April 23 five buds were marked. The blooming season was in its final stages, so I was unable to find more than five buds. Over the next 10 days, all but one of the five withered. The remaining head first opened on April 26 and repeated the next two days, following which its ray-like ligules protruded straight out from the involucre. These were somewhat smaller than with the earlier spring blooms.

At no point did the peduncle turn down in the manner noted for closed–head populations, if anything the peduncle seems to curve upward. Also apparent is the flexing of the peduncle during the open phases of the head, most likely a result of the heliotropic behavior of this population.

April 26 April 27 April 29

April 30 May 2 May 12

On May 15, following a heavy rain, the head was at a dispersal stage, with the peduncle more or less stretched close to the ground. The achenes had not fully developed. Perhaps this specimen was selected too late in the spring and should not be taken as typical.

Closed–head plants

On April 24 five buds in five different areas, representing two different types of floret morphology, were marked. At the time I was not testing for nodding behavior, so photos of the earliest stages were not made, the earliest being taken on May 2. Sequences for two heads are shown here, from early anthesis (May 2) through achene dispersal (May 16–19).

Head 1 (from a type with reduced but visible ligules). The head is already turning down by May 2, the downturn soon exceeding 180° in later stages. By May 16 the peduncle and head had turned toward an erect position and had already dispersed its achenes.

May 2 May 5 May 8 May 12May 16

Head 2 (from a type with vestigial ligules). Note that the head actually bends up a bit from May 2 to May 5, followed by the expected downturn of c. 180° in later stages. By May 19 the upper peduncle had turned upward at dispersal.

May 2 May 5 May 8 May 12May 16May 19

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