Thursday, August 22, 2013

Post flowering calyx throat closure in monkeyflowers

Once upon a time (not so long ago, 2012, in a certain esteemed tome which costs $125), about 15 species of monkeyflower were submerged under the name "Mimulus guttatus".  Such a broad treatment is equivalent to submerging species of pine as distinct as Monterey Pine (Pinus radiata), knobcone (P. attenuata), and Bishop Pine (P. muricata) into one species.  For these pines, this is the viewpoint circa 1880. Ignorance is not bliss in the realm of biodiversity conservation.   Many monkeyflowers are rare endemics, and our understanding of their distribution and abundance is primitive.

Erythranthe guttata sensu stricto is a perennial with stolons.  Within Section Simiola, most species have a feature of the calyx after pollination that is distinctive.  In flower, the calyx lobes are of two size orders: the upper is longer, the other 4 are about equal.  Following anthesis, in E. guttata, the lower two calyx lobes curve upwards, accompanied by an expansion of the inter-calyx rib tissues.

We have all seen the touch-receptive stigma of a monkeyflower (or if not, ought to...).  The pollination trigger mechanism in this instance involves a set of genetic instructions independent of those related to fruit maturation.    Fertilization triggers more than one genetic regulatory pathway: 1) quick, make seeds, and 2) even quicker, make the calyx differentiate.  How?

Most of the ca. 40 species of  Section Simiola, including E. guttata, have the post-zygotic calyx differentiation feature to variable degrees: eight species do not (E. utahensis, E. glabratus, E. arvensis, E. michiganensis, E. inamoena, E. geyeri, E. regni, E. visibilis).  

Images: above, two flowers, the lower post-zygotic and the upper at anthesis; below, the two same flowers, the lower post-zygotic.

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