M and I were camped in a clearcut in Loomis Forest (Okonogan county) in June, and found three different Ribes (R. cereum, R. lacustre, and R. viscosissimum) in full bloom within a ten foot radius. Despite being in members of the same genus, the flowers of these three species look very different. R. lacustre is bowl-shaped and brown; R. cereum is tubular and pink; R. viscosissimum is also pink, but has a showy ring of flared sepals around the tube.
My first thought was that these three similar shrubs must have different pollinators. How else to explain their floral diversity? The idea that pollinators drive the evolution of flower structure (The Grant-Stebbins model) is neither new nor edgy.
Just like with Darwin’s orchid, whose pollinating moth was not discovered until years after Mr. Darwin predicted its existence, there must be a creature that prefers each of these shapes, right?
North American Ribes are moneceous, with perfect flowers. Research on domesticated Ribes has shown that most Ribes are bee-pollinated; exclusion of pollinators significantly reduces yield.www.pollinator.ca/canpolin/gooseberries.html Though the stamens and anthers are positioned to discourage self pollination, it is known to occur. However, self-pollinated fruits often drop before ripening.
A study in California (http://humboldt-dspace.calstate.edu/handle/2148/1279) found that despite floral differences, the 14 species tested were all visited mostly by bees, though gnats, beetles and hummingbirds also stopped by. “Visitor assemblages varied as much between sites for individual species as they did between different species.”
Hybrid Ribes are unusual in the wild, though they are used in agriculture. An experiment In Latvia successfully crossed our Ribes sanguineum with their commercial black current (R. nigrum). Hybrids successfully bore fruit, and exhibited increased fungal resistance.
So, what have I learned from looking at these three shrubs growing and flowering together? They share at least some pollinators. Something other than pollinators is keeping them distinct. I’m not the first person to ask these questions. Maybe searches at a mollecular level will discover the answers. Maybe they will just raise more questions.