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Orobanche spp.

broomrapes

Orobanchaceae

Temperate Northern Hemisphere; Mediterranean, the Middle East, and central Asia

Attracts Pollinators

Native to North America

HardinessZones 5–10

Overview

Orobanche spp. is a genus of roughly 150 species of parasitic flowering plants in the family Orobanchaceae, distributed mainly across the temperate Northern Hemisphere, with centers of diversity in the Mediterranean region and western Asia. The plants lack chlorophyll and produce no green tissue; instead they attach to the roots of host plants through a swollen structure called a haustorium and draw water and nutrients directly from the host. Above ground, each plant is a fleshy erect stem 4-28 inches (10-70 cm) tall in shades of yellow, brown, purple, or straw, clothed in small scale-like leaves rather than functional foliage. Tubular two-lipped flowers, resembling those of snapdragons, are borne in a dense spike and range from cream and yellow to violet and purple-brown. Each plant can release tens of thousands of dust-like seeds that stay viable in the soil for many years and germinate only when they detect chemical signals from a suitable host root. Host range varies, with some species attacking a narrow set of plants and others parasitizing many. Several species, including O. crenata and O. cumana, are agricultural weeds that reduce yields of legumes, sunflower, and other crops across the Mediterranean and central Asia. Because the plants depend entirely on a living host, they cannot be cultivated as ordinary garden plants.

Native Range

Orobanche spp. is native across the temperate and subtropical Northern Hemisphere, with the greatest diversity in the Mediterranean basin, the Middle East, and western and central Asia. A smaller number of species occur in North America and Africa.

Suggested Uses

The genus is not grown ornamentally and has no garden uses; it is studied chiefly as a parasitic weed of crops and as an example of plant parasitism. A few species feature in botanical and ecological research on host-parasite relationships.

How to Identify

The plants carry no green leaves; the whole stem is yellow, brown, purple, or straw-colored and feels fleshy. Small triangular scales replace true foliage along the stem, which ends in a spike of tubular two-lipped flowers. Because they emerge directly from the soil over a host's roots and never form green tissue, they are unlikely to be mistaken for photosynthetic plants.

Appearance

Size & Dimensions

Height4" - 2'4"

Width/Spread2" - 6"

Colors

Flower Colors

Foliage Colors

Fall Foliage Colors

Bloom Information

Bloom Period

~6 weeks

Spring Summer

Flowering occurs mainly in late spring and summer, broadly April to August depending on species and host cycle. Each spike opens its tubular flowers from the base upward over several weeks. Seed capsules ripen soon after flowering and split to release very large quantities of tiny seeds.

Detailed Descriptions

Flower Description

cream, yellow, violet, to purple-brown

Foliage Description

yellow to brown scales; no green foliage

Growing Conditions

Water & Climate

Time to Maturity

Flowers within the season it germinates

Care & Maintenance

Care Guide

These plants cannot be grown by ordinary means, since they take all their water and nutrients from a living host root and die without one. They appear in gardens and fields where a compatible host is present, germinating from long-lived soil seed in response to root chemicals. In agriculture the genus is managed rather than cultivated, through crop rotation, resistant cultivars, and removal of flowering stems before they set seed. The dust-like seeds persist in soil for a decade or more, which makes established infestations hard to clear. No watering or fertilizing regime applies, because the host plant supplies the parasite. Management focuses on preventing seed production and on avoiding the movement of contaminated soil.

Pruning

Cut or pull the flowering stems before the capsules ripen to limit the number of seeds entering the soil. Because each plant produces vast quantities of long-lived seed, repeated removal over several seasons is needed to reduce an infestation. No pruning benefits the plant itself, which is generally treated as a weed.