Monday, March 10, 2014

Parasitic Plants

Cassytha filiformis is a parasitic, leafless, flowering plant fairly common in the beach environment. It is often noticed as yellow blotches growing near the sea coasts. There is also another group of parasitic plants in the genus Cuscuta, known as dodder. These parasites infest a broad range of plants throughout Hawaii as well as tropical areas worldwide.  They appear as small orange colored strands growing over the host plant.

Although these parasites have some green coloration (often masked by the orange color), which indicates that photosynthesis does occur, they are entirely dependent on other plants for their nutrition, water and even physical support.  They vine around their host and produce adhesive structures called haustoria which penetrate the outer layer of cells of the host and extract water and nutrients from the plants phloem and xylem tissue. The host is slowly being depleted of its nutrients and water, while the parasite garnishes nutrients to grow, flower and produce seed.

Some common names for this parasitic plant in Hawaiian are kauna’oa pehu, malolo and pololo. It can often be seen parasitizing tree heliotrope, beach naupaka, ohi’a, noni and screw pine as well as fruit producing trees like citrus, mango, avocado and nutmeg. The seeds can be transported great distances by ocean currents, tidal waves, birds, strong winds, even hurricanes, and by humans.

Heavy infestations can smother host plants causing a decline and even death of the host. C. filiformis is a threat to lowland reforestation projects. It is damaging and capable of killing native, endemic and naturalized coastal and woody plants.

There are some benefits to this group of plants.  Traditionally it has been used in Hawaiian ceremonies - worn as ornamentation and in decorative garlands or lei. It is valued for its diverse healing applications; in Fiji it is used to treat jellyfish stings and as a food source.
·        Manually remove parasitic plants, especially before seed production.
·        Fire has been used to rid an area of the parasite, but will of course kill or at least damage the host also. The same is true for herbicides which may be effective, but can also damage the host.
·        C. filiformis is intolerant of shade.
·         Grazing sheep will feed on this pest.

Photos by Forest and Kim Starr