Hemiparasitic. Now that’s an interesting word in the plant world, one I hadn’t encountered before, and I do love finding new words. But as usual when I discover something new, it led me down a rabbit hole to encounters I had not expected.
It goes along with another term — holoparasitic, which means a plant that is totally parasitic on another, completely depending on the host plant for nutrients and water. It can’t photosynthesize, lacks chlorophyll and cannot live on its own. One such is North American field dodder (Cuscuta pentagona) — stringy, leafless, yellowish-white viny stuff that can cover garden plants and perennials from late summer to early fall, and may also transmit plant diseases.
Most common in rural farming areas, it is spread by seeds and climbs up the stem of a plant to insert itself into the vascular system of its host. An often hardy annual, the only good control is destroying the affected plant. Pruning it out is generally not effective because even a small bit left in a living stem will regrow.
An interesting research find: Though a generalist — meaning it doesn’t select a single kind of host — dodder selects its hosts with the highest nutritional status using complex chemical clues. And we think we humans are so smart. Our noses often rely on clues from the nearest pizza restaurant or taco stand, which may not have any high food value at all.
We seldom encounter many true parasitic plants in our area; most native species are endemic to the West Coast and farther south. In piney forests, we might find ghost plant, aka Indian pipes (monotropa uniflora) — ethereal, waxy-white nodding flowers on delicate stems appearing to have been chanted into existence by elves at midnight under a full moon. I frequently found them in the Michigan woods of my youth and once tried to pick some, but I found that they turned black almost immediately.
Transplant attempts were unsuccessful. Years later, I learned they are not precisely parasitic but saprophytic, using a symbiotic relationship with fungi to extract nutrients from dead plant material in leaf litter or soil. Interestingly, parasitic plant flowers are pollinated by bees or flies, as is normal with most every other plant species, in spite of their unusual appearance; seeds are distributed by the wind, birds or ants.
Hemiparasitic plants, however, depend on a host plant only for water and minerals so that they can produce their own food through photosynthesis. In large colonies, they can affect the health of nearby plants by sapping them of necessary nutrients, and we often won’t understand a reason for decline in our perennials. Many are in the broomrape family, and because we recognize them as wildflowers, we don’t realize what those plant vampires are up to in the garden.
In some instances, hemiparasitic plants can be useful in controlling invasive plants by stunting them and slowing their spread. Mistletoe, marketed as Christmas decorations and vital for Christmas kissing, is our most familiar hemiparasitic example, found in topmost branches of oaks, sycamores and other hardwoods where it gets sun exposure. Mistletoe produces its own chlorophyll, but by siphoning water from host trees, it is considered parasitic.
It seldom harms mature trees. Rarely found in Missouri, it is often seen in Southeast Kansas, Oklahoma and Arkansas, hanging from trees in great clusters over rural roads and harvested by farmers and homeowners for sale at garden centers. Much commercial mistletoe we find for sale at Christmas is a dwarf European species introduced by botanist Luther Burbank to California in the early 1900s.
I once tried to introduce it to Chaos with seeds from local, fresh white berries as a bird would do, wiping them into cracks of oak bark, but nothing ever materialized. I suspect birds found them first. Mistletoe is not the only hemiparasitic plant in our fields and woods.
Two most familiar are native Indian paintbrush (Castilleja coccinea), coveted by gardeners for its brilliantly red, orange or yellow bracts; and lousewort, which grows wild in our own woods. Indian paintbrush is attractive to a host of pollinators, both as larvae and adults, including endangered checkerspot butterflies. It is also visited by hummingbirds.
Paintbrush’s parasitism occurs by attachment to roots of various grasses and forbs, including bluestem, blue-eyed grass and penstemons, making it difficult if not impossible to transplant let alone establish in a garden. Though considered edible and traditionally used medicinally by Native Americans, it has been found to draw toxic selenium from the roots of its host plants and should be used only with caution or avoided altogether. There are plenty of safe herbs and flowers available without decimating a rare wildflower.
Unfortunately, paintbrush, which was once common in Newton County, has mostly vanished from our area in the past decade. A beautiful field of it south of Joplin near where a landmark round barn was once located was plowed one year, and the paintbrush has not returned. It can still be found in prairies and protected conservation areas around the state.
Lousewort (Pedicularis canadensis), or wood betony, is often found in woodsy verges and fields — and in our own Chaos. I’ve only identified it as a native wildflower; the hemiparasitic term not even a mention in my wildflower books, which apparently are only in the business of identification and not properties of plants. It emerges in April with fuzzy maroon basal leaves, topped in late spring with a pinwheel of pale yellow flowers.
This one can live on its own but is an opportunist. I’m not nearly done learning about hemiparastic plants. Broomrape is a huge family with many wildflower members.
It’s going to be awhile before I see the light of day from this rabbit hole. That might require a lot of chocolate..
