An inflorescence of Lobelia spicata (A).

Flowers on female plants (B) have reduced, white anther tubes (indicated by the black arrow) that lack pollen, whereas flowers on hermaphroditic plants (C) have well-developed, blue anther tubes (indicated with white arrow) that contain pollen. 

In (B), the stigma is visible, but in (C) it has not yet protruded through the anther tube, and this flower is in male phase.

(left) John Stanton-Geddes ’04 with Lobelia spicata in Amherst, MA.

Reproductive ecology of Lobelia (Lobeliaceae)

Lobelia spicata and L. siphilitica (Lobeliaceae) are gynodioecious and populations consist of both hermaphroditic plants and male-sterile plants, although the frequency of male-sterile plants is typically quite low (ca. 10%) in Massachusetts (Miller & Stanton-Geddes 2007.pdf).  In this genus, male-sterility is believed to be under nucleo-cytoplasmic control and all male-sterile plants carry a cytoplasmic male-sterility (cms) mutation and no nuclear restorer.  In contrast, hermaphroditic plants either do not have a cytoplasmic male-sterility mutation, or have a cms factor but also have the appropriate nuclear restorer.

There are a number of questions in this system students could pursue including the discovery of multiple populations and a broader analysis of sex ratio variation among populations.  In addition, both species are sexually dimorphic and flowers on hermaphroditic plants are larger than those on female (male-sterile) plants; students could examine the nature of the dimorphism and investigate hypotheses put forth to explain sexual dimorphism in gynodioecious taxa.  Students interested in the evolutionary dynamics of cytoplasmic male-sterility mutations and nuclear restorers may also be interested in this system.