Bryant is the author of today’s entry:
A big thank you to Monceau@Flickr for today’s photograph of Matelea reticulata. Native to Texas and northern Mexico, netted milkweed or green milkweed vine is a deciduous perennial vine typically found in shrubby thickets on rocky hillsides. Matelea reticulata is placed in the subfamily Asclepiadoideae of the family Apocynaceae (dogbanes). Like many other milkweeds, plants of Matelea reticulata can host butterfly and moth larvae, including the monarch and queen butterflies.
Members of the Asclepiadoideae (a subfamily of the Apocynaceae) undergo pollination in an unusual way. The small pillar in the centre of the flower is known as the gynostegium. Unlike a “textbook” flower with individual stamens and a separate style with stigma, the gynostegium is a fusion of the stigma, style and stamens. Also, the pollen of flowers in the Asclepiadoideae are often stored in sacs, known as pollinia. These are generated near the base of the gynostegium, where the anthers are located. Insects are attracted to visit nectaries on the flower, and in doing so may have pollinia latch onto their legs. Upon visiting additional flowers, if the insect’s leg slips into a stigmatic slit (where the receptive surface of the stigma is located in the gynostegium), it can deposit the pollinium, and pollination occurs. The adaptive advantages of this approach remain under discussion, however the saying, “putting all of your eggs in one basket” definitely comes to mind. To see an example of hand-pollination in a milkweed, see this video on pollinium insertion.