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Thursday - March 01, 2007

From: Van Alstyne, TX
Region: Hawaii
Topic: Invasive Plants, Non-Natives, Herbs/Forbs
Title: Avoiding planting Indian Paintbrush in Hawaii because of invasiveness
Answered by: Joe Marcus


My daughter is living in Hilo, Hawaii. For her birthday, her boyfriend ordered her some Indian Paintbrush seeds. Trying to be sure she grows them correctly in a pot, she found instructions that say Paintbrush needs a "host plant" to be successful. What would be a good host plant for her to use? Thanks!


Parasitic plants come in several flavors. Among them, there are obligate parasites, which must parasitize a host plant in order to survive and receives all of its nourishment from the host plant. These plants typically lack chlorophyll. There are facultative parasites which will opportunistically parasitize a host plant given a chance, but can survive and complete its life-cycle without a host. These plants are often called hemiparasites or hemiparasitic plants.

Indian Paintbrush (Castilleja spp.) is typical of this group of plants. It can and will parasitize neighboring plants via root connections if living in close proximity, but will also grow and reproduce on its own if no host plant is available. The various species of Indian Paintbrush native to Texas often parasitize plants of the grass family (Poaceae), but they really aren't particularly picky about who their hosts are and will attach themselves to and draw nutrients from any number of plant species. Indian Paintbrushes growing with the assistance of a host plant will almost invariably outgrow a sibling without such benefits. Likewise, a host plant parasitized by a Castilleja will normally suffer quite noticably.

One species, Castilleja arvensis, native to Mexico, Central and South America has naturalized in Hawaii where it is found in association with, and parasitizing the Hawaiian native plant Dubautia scabra. Ecologists consider it invasive in Hawaii. Other Indian Paintbrush species could be similarly ill-mannered in the Hawaiian paradise.

We would urge your daughter to exercise great care and help protect the fragile Hawaiian ecosystem by ensuring her non-native species does not escape from cultivation. She can do this by using her flowering Indian Painbrush stems for cut-flowers and never allowing them to make seeds, or she could simply choose to not plant the seed at all and avoid the risk. After all, no one wants to be the source of an ecological disaster.


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