Portraits of Wildflowers

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Archive for August 5th, 2020

One strange Mexican hat

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On July 20th near the Taylor Draper entrance to Great Hills Park I came across one strange dude of a Mexican hat (Ratibida columnifera). It had way more ray florets than a Mexican hat is supposed to have, and for once fasciation didn’t seem to account for it. Oh well, we take our weirdnesses wherever and however we find them.

I’m thankful to Dr. George Yatskievych at the University of Texas for providing an explanation: “Replacement of flowers is a bit different process [than fasciation].  Each meristematic cell on the receptacle produces a set of cells with the potentiality to become either a ray or disc floret.  Regulatory developmental genes in more than one gene family determine the outcome of the differentiation…. This accounts for ‘rayless’ mutants, as well as heads in which part of the disc has become replaced with rays.  This includes so-called ‘doubled’ heads in groups like zinnias and dahlias that have extra cycles of rays toward the periphery of the disc, as well as odder mutants with rays appearing in an atypical locations, such as the center of a disc.  In some cases, this switch to a different floral morphology is caused by something that disrupts normal development of the head (such as insects or micro-organisms), but in other cases there is a genetic mutation (in which case the plants will tend to pass the mutation to at least part of the next generation).  One of the more interesting mutations that I have seen pops up occasionally in Gaillardia, in which the marginal florets have corollas that are enlarged, but are still basically shaped like a disc floret at their tips. The bottom line is that there can be more than one cause, but it always comes down to the expression of regulatory genes during floral development.”

© 2020 Steven Schwartzman

Written by Steve Schwartzman

August 5, 2020 at 4:45 AM

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