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Excerpts from Jim Conrad's
Naturalist Newsletter
page October 12, 2014 Newsletter issued from the Frio Canyon Nature Education Center in the valley of the Dry Frio River in northern Uvalde County, southwestern Texas, on the southern border of the Edwards Plateau; elevation ~1750m (~5750 ft); N29.62°, W99.86°; USA
IVY-LEAF MORNING-GLORY
The next morning I broke camp before the sun rose above the hills to the east, but when already enough light shone to see my way. With the new tent in my backpack I stepped off the massive layer of Cretaceous Edwards Limestone capping the hill and suddenly found myself beside a blue morning-glory flower glowing with more ethereal light than seemed possible for such a still-dark morning. That's it above.
Though I'd not seen this species here during my two-year stay, I thought I knew who it was, for back in Mississippi such a blue-flowered morning-glory with three- and five-lobed leaves put on real shows when entangled in fences and twining over roadside bushes. But other morning-glory species also can produce blue flowers and deeply lobed leaves, so I checked more features.
First, notice the long, slender sepals, or calyx lobes, from which the corolla arose, paying special attention to how long hairs at the calyx base and on the flower stem, or pedicel, face backward. That important field mark is shown below:
Also the blue flower's throat is white, not dark, and the pollen-filled anthers cluster close to a three-parted, biscuit-shaped stigma, as shown below:
It's the Ivy-leaf Morning-glory, IPOMOEA HEDERACEA, native to South and Central America, Mexico and the Caribbean, and occurring extensively as a weed in eastern North America, and the southern parts of the western US. In the US, genetic sequencing suggests that the species was introduced fairly late in its evolutionary history, though it's been here long enough to be listed as native by most experts.
In our area there's a commonly occurring, very similar species, the Purple Morning-glory, which we've profiled at http://www.backyardnature.net/n/h/purpurea.htm.
The Purple's presence is worth mentioning because the two species are so closely related that cross pollination can occur when they're near one another.
A 2008 paper by Robin Ann Smith and Mark Rausher in The American Naturalist reports that the Ivy-leaf's seeds produced through cross pollination with Purple Morning-glories are sterile. However, the Ivy-leaf's pollen doesn't germinate on the Purple's stigmas and so the Purple's seeds don't become sterile. In terms of competition for resources, this cross-pollination situation affords a big advantage for the Purple.
However, our Ivy-leaf Morning-glory defends itself with something called "character displacement." When Ivy-leafs occur along with Purple Morning-glories, the Ivy-leaf's flowers tend to produce stamens whose anthers tightly cluster around the stigma, exactly as our last picture shows. Presumably this reduces the possibility of cross-pollination with Purple Morning-glories, plus the nearness of the anthers possibly increases self-pollination. Self pollination isn't as desirable as being pollinated by another plant of the same species, but it's better than having one's seeds killed by cross-pollination.
When Ivy-leaf Morning-glories occur alone, flowers are produced with anthers more loosely gathered around the stigma.
Well, this is a wonderful way to end my naturalizing days in Texas: Such a very pretty flower, completely unexpected, and with such a fascinating story.
It's been a good stay here, and I'm glad to have this flower as a symbol for my last days in Texas.