Wild Basin Nature Preserve, Arroyo Vista Loop, walk 10/18/19

My summer of rediscovering Texas flora was interrupted in June by an injury requiring foot surgery. In early October, I was cleared to put full weight on my foot (in a surgical boot) and walk on uneven surfaces, but today (4 months later) was the first day since then that walking outside has been an option. We’ve either had slip-and-fall-risk terrain from rain or heat-stroke weather with temperatures approaching 100F and high humidity. Because the idea of walking around my neighborhood on concrete in a surgical boot was unappealing, my husband, a friend, and I went to a nearby greenbelt, Wild Basin Wilderness Preserve on Loop 360 in Austin, TX. Its accessible trail, the half mile Arroyo Vista Loop, was a challenge for my wobbly ankle and stiff arch. I remember that when my dad visited years ago, the path was smooth, flat, and well mulched. Apparently when I walk with more sure-footed people, I pay much less attention to the trail’s maintenance, so I was surprised to see that the years had not been kind to the trail footing. But I survived.

A birthday party of elementary school girls thundered past us throughout our walk, but I was unable to work up any outrage for the noise. Mostly I enjoyed the clean smell of nature, admired and photographed the plants, watched the occasional butterfly flit by, and glimpsed a few insects and spiders before they disappeared. Butterflies were small yellow Sulfurs (?) and a few Monarchs passing through on their way to their wintering grounds. Boot-encumbered old ladies with cell phone cameras aren’t going to photograph butterflies on a rocky hillside, so you’ll just have to take my word for it.

My favorite observation today was a fine textured twining vine with small, narrow leaves and minuscule flowers. I could see it had tiny white flowers but I needed the zoom screen on my phone to have a clue about their shape and I had to see it on my tablet to really see its features. I've tentatively IDed it as an Edwards Plateau native,
Bearded Swallow-Wort, Metastelma barbigerum. It’s easy to see, with extreme magnification, why it’s called "bearded." Don’t know about the swallow-wort part. Maybe it’s something to do with sore throats...
https://www.inaturalist.org/observations/34568932

Looking up this plant led me down a dark path. Two European species of swallow-worts have become a well-researched, invasive scourge on wildlands and fields in the eastern US 🍁🍂. Both Black Swallow-wort and Pale Swallow-wort are aggressive vines that can form a solid canopy or fill up a field by twining up itself, which isn’t good for the plants they compete with for light, water, and nutrients. Their roots give off allelopathic compounds that prevent or reduce the germination and growth of other plants, including native milkweed species that are the “proper” larval hosts of Monarchs and many related butterflies. They’re also larval trap plants, meaning that the adults will lay their eggs on the invaders but the larvae die because their host plant doesn't nourish them. Talk about three strikes for the Monarchs!

I didn’t learn whether M. barbigerum is a good, bad, or indifferent host for Monarchs, although other native Metastelma species are acceptable hosts for other butterflies. But I did learn something about climate change and the milkweed/Monarch relationship 🐼. It’s fairly well-known that Monarch larvae accumulate toxins from their host plants for defense against predators and parasites 🍃 🍁 🍂. But it was news to me that when the plants grow in warmer temperatures, they produce too much of the toxin, which reduces the vigor of the larvae and adult butterflies. Plus, when CO2 levels rise, the toxins become less effective at protecting against parasites 🌿. This is bad news about climate change that I had somehow overlooked.

Taxonomically, swallow-worts are milkweeds. You probably figured that out for yourself because they’re Monarch hosts. They’re in the Milkweed subfamily (Asclepiadoideae) of the Dogbane family (Apocynaceae). Wait, you hadn’t heard about the dogbanes absorbing the milkweeds? That’s OK. Except in botanical circles, it didn’t make headlines. In the taxon scheme iNaturalist uses, the European invaders are in a different genus than “my” swallow-wort: Cynanchum versus Metastelma. But in other schemes, the Bearded Swallow-wort is lumped in with them as Cynanchum barbigerum. I’m glad iNat keeps up with taxon juggling for me and Google makes it easy to look up obsolete names.

If you feel like exploring or IDing, here are my observations:

I’d be overjoyed if someone who knows Harvestmen, bees, or mites would look at my arthropods

References