C. carduacea heads in bud & in flower, but which are which?.

Bud Orientation with C. texana & C. carduacea

by Bob Harms 

The head in bud is found in virtually all possible alignments — ‘nodding’, cernuous, ascending, erect. But unlike the head at anthesis, it does not exhibit diurnal rising and falling.

The images below do not reveal any significant difference in head alignment for the two species. The youngest bud head is directed upward, with no apparent peduncle having developed. As the peduncle develops, rather quickly, the erect head alignment may persist a short while or begin to bend over, at times to as much 180°. As the bud develops and the peduncle lengthens there would seem to be two stages: first the head nods ca. more than 90° and later begins to rise to ascending or even erect orientation just prior to the onset of anthesis — as in the images at the bottom of this page.

A number of explanations for this sequence of events would seem possible.

• The cells of the peduncle below the head are programmed to grow in an asymmetrical manner, thus forming a bend. But with rapid lengthening of the peduncle in later bud stages and during early anthesis this asymmetry is interrupted, leading to a rising head/peduncle orientation. The peduncle often lengthens as much as 2 cm per day as the somewhat ‘gangling’ stalks in the image at the top illustrate.
• On the other hand, the peduncle is programmed to grow straight, but is bowed downward by the weight of the head, which can be seen to be well developed prior to growth of the peduncle.

C. texana

C. carduacea

Advanced Buds (to Pre–anthesis)

C. texana	C. carduacea	C. carduacea	C. carduacea