Plants are often viewed as docile, near inanimate life forms. They appear to grow in relative harmony with each other, with the occasional fast-growing individual shading out its neighbors.

However, there are many forms of relationships that all living things participate in, and plants are no exception. Some can be predators like the Venus flytrap. Other plants can be parasites which derive part, or all their nutrient requirements from a host. This lifestyle is not common and makes up only 1.2% of all flowering plants. It has evolved independently in 12 separate lineages, and each time it has been dependent on the development of one structure — the haustorium.

Haustoria can develop on either the stems or roots of the individual. This specialized organ aids in the attachment, invasion and eventual transfer of nutrients from the host to the parasite. But it is a long road from attachment to the formation of the xylem bridge, which is the direct connection to the host’s structures that carry both water and sugars.

The haustoria must break down cell walls to penetrate the host and avoid the individual’s immune response. Part of this response is sending chemicals into the parasite via this direct linkage that turn off certain genes which reduces the individual’s viability. Understanding this process may allow for a novel means to control parasitic plants in the future. This is important because some species cause serious losses in crop yields. The plant species impacted depend on the parasite. Some require a specific host, while others are generalists.

Host selection often varies by lineage. For example, Korthalsella (hulumoa or kaumahana), our native mistletoe, has specific species they will use as hosts. Surprisingly, native sandalwoods are also parasitic plants. However, they only require partial nutrients from their hosts, making them hemiparasites.

Native species Cuscuta sandwichiana (kaunaoa kahakai) does not have a specific host, but the plant is dependent on parasitizing one or many plants. Species of Cuscuta, also known as dodders, have only 10% of the chloroplasts, organs that convert sunlight into sugar, that other flowering plants have. This means without a host they will not survive and are referred to as holoparasites.

So how do these plants find their hosts? In some lineages seed germination is partially induced by the same chemical that plants use to attract beneficial fungi.

Growing at home

Adding a parasitic plant like a dodder to your yard is a unique way to observe parasitic plants, grow material for lei and possibly a low maintenance way to control weedy areas or kapakahi lawns. Unfortunately the naturalized species C. campestris is more common than the native species. It is often seen along sandy roadsides in Kaimuki — just look for a mass of orange, leafless stems.

If you are looking for the native species remember that it is never acceptable to remove them from protected areas. To tell the difference between the two species you need to examine their tiny blossoms. The flowers of the native species are larger, measuring 3-4 millimeters, sometimes up to 5 millimeters long with erect petals. Also the calyx, a whorl that encloses and protects these petals, has triangular lobes.

Once identified put your cuttings on the desired plants and make sure to keep them moist until they become established. After that, water is rarely needed. Dodders thrive in full sun and can tolerate dry periods, salt spray, heat and winds. Obviously, this is all dependent on health of the host plants. It is important to keep both species of Cuscuta away from your valuable plants. Otherwise it will harm them too. Finally, make sure to keep the patch in check by pruning it back.

Jesse Adams is a botanist at the Harold L. Lyon Arboretum, where he works to catalogue, propagate and conserve the plant diversity found there.