This post was written by Hubbard Fellow Mary Parr. Mary has a strong interest in botany and has picked up the local plant species around here very quickly. If anyone is looking for someone to do plant surveys or seed harvest next season, she would be great at it! (…but you can’t have her until February)
Of the many new plants I have observed on Platte River Prairies, the most fascinating has been an unusual parasitic one. It was early summer when I was first struck by its appearance – a gnarled mass of neon orange silly string entangling a 6×6 area of plants. Shocked at this vivid spectacle, I investigated further, finding no leaves or connecting stem to the ground! What was this botanical blasphemy?! Well, I’ll tell you what it is. It is Rope dodder (Cuscuta glomerata), otherwise known as wizard’s net, devil’s guts, strangleweed, witch’s hair, or my personal name for it – “orange spaghetti plant”. All dodder species are obligate parasites, meaning they bear no photosynthetic material and rely completely on a host to complete their life cycle. While many people consider parasitic organisms sinister, I revel in their amazing strategies of survival!
Listen to this! Rope dodder begins its life cycle in the soil as a seed like any other plant. From the first moment of germination, it is relying completely on its limited stores of energy in its embryo and immediately begins to search for a host. The first emerging strands literally sniff out their hosts by their scent! They use specialized chemosensory cells that can identify airborne volatile organic compounds from their preferred host and grow towards them. Rope dodder has been noted to prefer sunflowers and goldenrod in the Aster family. Once a host is identified, the plant will immediately start to twine around the stems. Rope dodder then begins to invade the plant tissue, working its way into its vascular system. It does this by utilizing two different modified root-like structures called haustoria. The first form will invade the water transporting xylem, and the second will target the sugar carrying phloem. Rope dodder will then completely abandon its own root system, living unattached to the ground! How crazy is that? Wait there is more!
When time for reproduction comes around, the orange spaghetti strands will wither and vanish leaving only spiraling dense inflorescences on the host stem. Some select species of wasps (Hymenoptera) have been identified pollinating the tiny flowers. The seeds of the dodder genus have very robust seed coats enabling them to persist in the soil for up to 20 years! Dispersion mechanisms of the seeds are widely discussed. Largely, the seeds will fall in the area below the plant, but occasionally are dispersed through water movement, the gut of herbivores, humans, or our field equipment.
Seed transmission for some species of dodder is very bad. A majority of the 50 dodder species in North America are considered noxious weeds and can cause significant economic damage on agricultural and horticultural crops. While a parasitic plant may not kill its host, it will weaken its ability to resist other pests, fungus, and diseases. Dodder has even been found to transport diseases among plants as it is connected to its vascular system! (Unfortunate for the host, but still pretty cool right?) While many dodder species are considered noxious, there are remaining native species that are uncommon and even threatened in some states. These rarer forms of dodder have been used as site health indicators. Rope dodder is one of the native species that largely grows in the Midwest in prairies, open roadsides, and mesic areas.
In our prairies, we don’t see rope dodder as a threat because we barely see it at all. The patches are far and few and a fun surprise to find when walking through the prairie. We have no shortage of goldenrod and asters, and in some areas could use a bit of competition. Largely, rope dodder is adding heterogeneity and diversity to the landscape.