Baccharis halimifolia and local relatives
(Baccharis comes somehow from Bacchus, the god of wine. Halimifolia refers to a different plant with similar leaves.)
Working in the Kiplinger Natural Area in Stuart, Florida, today, John and George enjoyed a dozen wildflowers in peak display, so beautiful: White-Snakeroot, Bluecurls, Liatris, Coin-Vine, and so many more. In the garden of native delights is a fall-flowering species with curious attributes, Saltbush, Baccharis halimifolia. In our area we have also Baccharis glomeruliflora (flowers in tight clusters) and B. angustifolia (narrow untoothed leaves), representing a widespread genus of over 350 species.
For starters, the distribution of Baccharis halimifolia is odd, with a population in eastern Canada, then a gap of over 400 km to New England, down the U.S., into the Caribbean and Mexico. This is one widespread plant. And then some: it has escaped cultivation or otherwise invaded around the globe, even in the Mediterranean and in Australia, where it is a pest battled with a destructive rust fungus. The species is not welcome in many places because it accumulates in pastures and is fatally cardiotoxic to some grazers. I don’t know where the poisons reside, but the leaves have secretory glands probably responsible for protective secretions.
The individuals are separate males and females (proper term, dioecious, die-EE-shus). That’s no biggie, but the odd thing is, how many dioecious plants have male-female differences other than the flowers? That is rare in my experience. According to a USDA publication, the males have longer shoots, softer leaves, faster growth, and earlier seasonal senescence than the females. Sounds like maybe the males are more “designed” to reach out and scatter pollen, in contrast with females who need more sturdiness and an extended season to make fruits. Pollination is by wind and by insects. The small wind-dispersed fruits are on parachutes.
Species of Baccharis have an adaptation sometimes associated with salt-tolerance…water-emitting valves called hydathodes at vein tips. Hydathodes resemble the drip-emitters used in irrigation, flushing out water and anything in it such as excess salt.
John and I have been watching ants scramble around the Saltbush. The ants come marching two by two to tend sucking insects. The sucking insects we’ve seen are aphids and perhaps two species of scale insects. (Baccharis is the main Florida host for Green Scale.) Such insects “suck” sugary sap from the host plant. The sugary goo passes through the lil’ sucker to drip forth from the other end as “honey dew.” The honeydew can spread and grow black fungi called sooty mold, and some of it follows a more interesting path as ant food.
That ants crave honeydew and tend its makers like farmers tending cows is well studied, producing conversations about three-way symbiosis: win-win-win. The plant gains armed guards. The ants get sweet treats. And the sucking insects, well, if they are not merely exploited, might get help in dispersal and might be under the protection of their creepy little shepherds.
CLICK to see a similar symbiosis, of all things, on the inside the stem of a different plant.