Gardening in Tucson
and Southeastern Arizona

Parasitic Plants

Castilleja: Indian Paintbrush
Flower brachs are red or orange, or rarely, other colors. The petals on many species form narrow tubes, often yellow or greenish. Paintbrush commonly blooms late winter, spring or summer. A semi-parasite, paintbrush is always found with a companion plant, very often grass. Most are short-lived perennials. Species native to Arizona include: Castilleja austromontana Rincon Mountain Paintbrush, Castilleja exserta Owl's Clover (annual), Castilleja integra Wholeleaf Paintbrush, Castilleja lanata Sierra Wooly Paintbrush (pictured) and Castilleja tenuiflora Santa Catalina Paintbrush. These plants are said to attract hummingbirds.

Cuscuta: Dodder is a parasite that looks like yellow string entwining a green plant. Its roots infiltrate the stems of a host to derive nourishment. It will attach to almost any plant species and some vegetable crops can be devastated. Dodder may ensnare several adjoining plants and has been shown to transmit viral diseases.

Fifteen Dodder species are present in Arizona. The one described here is common to the southeastern Arizona desert.

Its stems may be yellow, orange or white in color. It produces small white spherical flowers, appearing mainly July through September. Seeds are distributed by wind or by the manure of animals. Seeds can remain in the ground for up to five years before germinating. When it sprouts, the Dodder vine will find the stem of a nearby green plant, attach itself, and detach from its own seedling roots.

Eradication is achieved only by cutting the host (green) plant to the ground. Native plants will grow back. Dodder grows quickly and early eradication is best. Constant vigilance is required once a single infestation is found.

Phoradendron californicum: Desert Mistletoe is a perennial parasite occurring mostly on leguminous trees such as Acacia and Mesquite. Velvet Mesquite is especially susceptible. A partial parasite, Desert Mistletoe is capable of photosynthesizing, but its roots invade the bark of the host plant and take in water and some nutrients.

Desert Mistletoe has narrow scale-like leaves resembling a clump of grass that can be green, yellow-brown or brown. Its flowers are tiny and yellowish-green.

The fruit is a pinkish-orange, non-sticky berry that ripens between October and December. Birds feed on the berries, which turn sticky in their digestive tracts, and disperse the seeds to the bark of trees.

This parasite can kill its host tree over many years. One treatment is to cut off the branch of the tree 1' to 3' below the attachment point of the Mistletoe when the parasite is first noticed. However, the Mistletoe can reappear. Once the Mistletoe is as large as that shown in the photo, it may be necessary to cut the host tree to the ground. Both Acacia and Mesquite trees will re-sprout from stumps. There are no chemical treatments.

Krameria parvifolia: Range Ratany has odd-shaped flowers that bloom spring to end of summer. A sprawling, tangled low shrub, it is semi-parasitic, getting water and nutrients from the roots of other plants, apparently without harming them. Nutlike fruits are hairy and covered with spines.