Reproduction in Plagiobothrys nothofulvus

While not much is known about the life history and reproduction habits of Plagiobothrys nothofulvus in particular, it can be assumed that its mode of reproduction is similar to that of other angiosperms, especially those that comprise its family, Boraginaceae.  Two genera that fall into the same family as Plagiobothrys, Lithodora and Glandora, rely on interactions with various pollinators to be able to produce their flowers (Ferrero et. al 2011).  Pollination may also be accomplished by wind.  Pollination is extremely important to P. nothofulvus because it allows for the transfer of pollen from the stamen (male reproductive organ) to the pistil (female reproductive organ) (Campbell et. al 2008, UC-Clermont Biology 2014). 

The stamen is comprised of a filament ending in an anther (UC-Clermont Biology 2014).  The anther is where the male gametophyte is formed; this gametophyte is known as a pollen grain.  Four pollen grains are formed when a microsporocyte, diploid cell in the anther undergoes meiosis (Campbell et. al 2008).  The pollen grains, in turn, are comprised of a large, vegetative cell and a smaller germ cell, the latter of which eventually divides mitotically to produce two sperm cells (Campbell et. al 2008). 

Multiple stamens surround the flower’s pistil, or female reproductive organ.  At the top of the pistil is the stigma, which is sticky to help pollen grains from the anthers attach (UC-Clermont Biology 2014).  The ovary contains an ovule, which is where the female gametophyte is formed via meiosis.  This gametophyte is known as the embryo sac, and is one of four daughter cells created when the megasporocyte undergoes meiosis.  In meiosis in the ovary, only one daughter cell goes on to become a gametophyte, while the other three simply disintegrate (Campbell et. al 2008).

Once a pollen grain comes into contact with the sticky tip of the stigma, the grain develops into a pollen tube, which grows to extend down the body of the ovary, also known as the style, until it reaches the ovule (Campbell et. al 2008).  Here, each of the two sperm cells generated in the pollen grain fuse with the two of the nuclei of the female gametophyte. One fusion results in a diploid zygote, while the other results in what will later become the endosperm of the seed.  Double fertilization is actually really clever since it ensures that endosperm won’t develop in ovules without fertilized eggs, which would be a huge waste of energy (Campbell et. al 2008).  

After fertilization occurs, a seed develops within the ovule.  The seed is made up of three main parts.  The first part is the plumule, which consists of two baby leaves and the meristem.  Next are the either one or two cotyledons, which act as the zygote’s source of food (UC-Clermont Biology 2014).  Plagiobothrys nothofulvus is a dicot because it has two cotyledons (Calflora 2014).  Finally, the seed contains a hypocotyl and a radicle, which develop into the lower stem and the roots of the plant respectively (Campbell et. al 2008).

Of course, none of this process would be possible without the flowers’ pollinators.  For Plagiobothrys nothofulvus and other members of the family Boraginaceae, these typically include bees, flies, and insects from the order Lepidoptera such as Proserpinus clarkiae, which is mainly comprised of moths and butterflies (Zomlefer 1994).  Without these vital interactions, P. nothofulvus would not be able to reproduce!  Like many other flowers, it has mechanisms to prevent self-fertilization, which would decrease genetic diversity.

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