Glade Lobelia

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Glade Lobelia

30 Sep

Lobelia glandulosa

Campanulaceae

So nice to get out into the flooded (Hurricane Ian) marsh after a long trip complete with Covid. A species comfortable in a flooded marsh is Glade Lobelia, blossoming now in a foot of water. Back in 2014 it appeared in this blog, but today we’ll focus on a different angle, the fancy way the flowers work in this and other Lobelia species.

The male pollen-making anthers are united into a tube around the female pollen-receptive stigma. Think of me pulling on a turtleneck sweater: the anther tube is the sweater neck, and my head pushing through the tubular neck is the stigma. The combined anther tube juts out of the entrance to the flower.

Looking into the flower. The black unit at the center is the anther tube.

Male and female unit removed from flower. The tube (matching the black in the photo above) is at the upper left, with two stigmas sticking out its tip.

Pollination happens in two phases, male first. At this first stage the anther tube produces pollen to its inside. The pollen is then plunged out of the tube by the rising still-unreceptive stigma. The pushed-out pollen is exposed at the tube tip to be picked up by floral visitors. A second force no doubt helping to squeeze the pollen forth may come from bees squeezing the anther tube while pushing past it to enter the flower. If you squeeze the tube with your fingers yellow pollen comes out the end like toothpaste from its tube.

Squeeze the tube and yellow pollen comes out.

After the pollen release, the female phase takes place as the stigma rises beyond the tip of the now-empty anther tube. Upon emerging from the end of the tube, the now- exposed stigmas spread out to accept insect-borne pollen from other flowers.

Self-pollination is avoided in Glades Lobelia by the separation in time of two phases. But in some species self-pollination is a “plus.” In Lobelia all that is needed for self-pollination to happen is for the stigma to become receptive while squeezing the pollen out. That is, allow the two phases to overlap in time. Nobody knows how often this situation has evolved, but there is one obvious case in Lobelia where the separation in time is documented to have broken down: In Lobelia inflata (Indian-Tobacco) the stigma is fertilized by self-pollen while still in the anther tube. That being so, the tube never opens, and the self-pollinated stigmas never emerge from it. Everything is self-contained.