Chaptalia texana Open Heads & Diurnal Cycle
by Bob Harms  email-here

A C. texana population of some 50 plants with heads that open with well exerted ray-like flowers in March–April 2010 was observed to undergo a diurnal cycle of opening and closing, individual heads repeating this cycle over a period of several days. Although most heads had ceased to open by late April, one late head, with somewhat shorter ligules, exhibited this pattern for three days, 26—29 April, followed by a closed head with ligules exerted directly out of the involucre — shown directly below.

April 26 April 27 April 28
April 29 May 2 May 6

On April 3 the same head for 2 plants was photographed at 5 times between 9 a.m. and 7 p.m [sunrise was at 7:18; sunset, 7:52]. Both were on the west-facing hillside in a relatively narrow canyon in locations that were sunny for most of the day, with slight differences. Plant 1 was some 75 ft higher on the hillside than plant 2, which was along a trail at the bottom of the canyon.

time plant 1 plant 2
9 a.m. 9 AM 9 AM
12 p.m. 12 PM 12 PM
3 p.m. 3 PM 3 PM
5:30 p.m. 5:30 PM 5:30 PM
7 p.m. 7 PM 7 PM

What controls this cycle? Not light?

This is discussed on a separate page.

Plant Resources Center Home PageFlora of TexasChaptalia texana