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Iris x robusta

Botanical Name: Iris x robusta (added by D. Kramb, 10-NOV-03)

Botanical Synonyms:



Spec-X, interspecies hybrid (D. Kramb, 10-NOV-03)

Common Names:


Chromosome Count:

2n=90 (D. Kramb, 01-SEP-04)

General Description:

Iris robusta is apparently a naturally occurring hybrid between Iris virginica and Iris versicolor. (D. Kramb, 19-JAN-04)

Plants form dense clumps. Foliage is dark green, stiff with mid-rib, 28" to 32" tall and 1/2" to 3/4" wide. Stalks have 2 to 3 branches with 3 buds per branch, 30" to 36" tall. Flowers are intermediate, later than versicolor, but earlier than shrevei and are better and longer lasting. Standards are more or less the same as in versicolor, upright or flattened, lighter in color than the falls. The falls are larger as in shrevei, horizontal, tips slightly pendulous, depp purple to violet. There is little variation in the same colony. Styelarms are purple in the center and bordered white or pink. Seedpods are cylindrical, sharply triangular, less than half the size of pods of shrevei, and narrower than versicolor. Seed ripens later than versicolor but earlier than shrevei. Seeds are slightly corky, rounded or D-shaped. Seeds are smaller than shrevei, and light brown. They germinate after frost treatment and seedlings will bloom in the second year. (D. Kramb, 01-SEP-04)

Distinguishing Features:

The stems and foliage often exhibit black coloration, especially in early spring. (D. Kramb, 19-JAN-04)

Preferred Habitat:

Grows best in full sun with wet soil, such as on the edge of a pond. (D. Kramb, 19-JAN-04)


Estimated Zones 4-9. (D. Kramb, 19-JAN-04)

Native Range:


Status in the Wild:


Commercial Availability:

Specialty nurseries and water garden centers. (D. Kramb, 19-JAN-04)

Sources Cited:

Information entered on 01-SEP-04 comes from issue# 60 of the SIGNA bulletin, page 3118. The article was written by Tony Huber of Laval, Canada. (D. Kramb, 01-SEP-04)

Additional Comments:

Robustas may occur naturally in places where versicolor and shrevei populations overlap. These hybrids tend to give nicer and more vigorous plants when shrevei is 2n=72. When shrevei is 2n=70 the back-crosses are short-lived and sterile due to the unpaired chromosome combination. (D. Kramb, 01-SEP-04)

Where to buy it:

Chapman Iris

Hildenbrandt's Iris Garden

SIGNA member!

Impressive Irises

Iris City Gardens

SIGNA member!

Joe Pye Weed's Garden

SIGNA member!

Plant Delights Nursery

Siberian Iris Gardens

SIGNA member!

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