Another Weed from Hell

Not all noxious weeds are exotics. Native species can be just as unwelcome! You'd think I'd have learned by now to be suspicious of any new plant popping up in the yard, because so many have turned out to be pests. No, I wait until I've got an infestation before I decide they are unwelcome. 

 I first noticed Galactia, or Milk Pea, twining around some Pink Muhly Grass. It didn't seem to amount to much, and it  had a rather sweet little pink flower. I forgot all about it. Big mistake. They may seem delicate and innocuous, but they become a menace in a very short time due to their robust production of mostly-viable seeds. They twine around any and all support, blocking sunshine, and wrapping so tightly around stems that in some cases they start cutting off circulation. A good healthy vine has no trouble pulling a small-to-medium woody branch downwards.

Stems with the diameter of large thread prove surprisingly strong.  Over time the vine develops a relatively deep, carrot-like taproot, a series of taproots, or even a kind of colony of roots. Even in sandy soil it isn’t easy to dig them out.( Because of the long taproot, milkpea species would likely regenerate quickly after brush fires). It gets even more complicated when you want to avoid too much damage to the infested plant you want to save. Digging and pulling hurt the plants you want to save. Herbicide will kill the leaves, but the plant regenerates from the deep roots. And it is very difficult to avoid getting any herbicide on the "good" plant.

 After reading Guy L. Nesom's, Taxonomy of Galactia (Fabaceae) in the USA, (link below), I've concluded that the milk peas in my yard are either Galactia regularis, Galactia volubilis, or both. According to Nesom the taxonomy of Galactia is somewhat confused, even controversial, especially so when it comes to these 2 species. Both have alternate, 3-foliate leaves, with fruits and stems displaying varying degrees of hairiness. (A 3 foliate leaf looks like a cluster of 3 leaves, but actually is only 1. Lots of species in the "Bean" family have this characteristic).

The weed(s) show great variation in size in my yard, depending on exposure to sunlight and general growing conditions, and I made all  my drawings and sketches from different plants at different times before I realized I might be dealing with more than 1 species. However, the species in the drawing most closely resembles G. volubilis, due to its long flowering stalk, size of flower, and mostly oblong-to-lanceolate leaf shape. The seedpod as drawn may not be typical.

 According to Nesom's article, Milkpeas are widespread in Florida and much of the United States. The genus occurs mainly in the Americas, especially the southeast and south-central US, West Indies and Mexico. Four species are native to Asia, Africa and Australia. The genus name is derived from the Greek galaktos, “milk,” due to the milky sap in some species. (The Florida species do not have milky sap).  Nesom lists 21 species for the US, with 13 represented in Florida.

 Several plants of in a pot with a trellis could make an attractive display, and the flowers attract numerous small pollinators. However, great care would be necessary to keep it from spreading, given the  high germination rate of the seeds.  Birds and possibly insects eat the seeds. Grubbing animals like skunks might be able to  eat the smaller taproots, but it would take some "chompers" and cast-iron digestive system to get anything from the taproots once they become woody.

Milkpea is a legume, and most legumes are associated with nitrogen-fixing bacteria in their roots. So far I haven't been able to ascertain whether local species of Galactia are associated with such bacteria, though I haven’t seen any typical root nodules.

Minno and Minno (1999) list the milkpeas vouchered for Collier County as larval host plants for Ceraunus and Cassius Blues, the Gray Hairstreak, Silver Spotted Skipper, Zarucco Dusky Wing Skipper and the Long-Tailed Skipper. 


 Apart from personal observations or as otherwise noted, the information in this article is derived from Guy L. Nesom, (Fabaceae) in the USA. Phytoneuron 2015-42: 1-54. Published 15 Jul 2015. ISSN 2153 733X.  

Marc and Maria Minno. Florida Butterfly Gardening. University Press of Florida. 1999.