Iris dichotoma (also known as Vesper iris) is a species in the genus Iris and is also in the subgenus of Iris. It was once formerly known as Pardanthopsis dichotoma as it was placed in a genus of its own before DNA testing resulted in it returning to the genus Iris. It is native to the forests and grasslands of Siberia, China, Mongolia and Korea. It has long greyish green leaves, long branched stems carrying many flowers in summer or late summer. In shades of violet, mauve to purple, lavender, pale blue, white or pink. They appear in the late afternoon at the time of Vespers (a service of evening prayer).
Description
Iris dichotoma grows from a small fibrous rhizome, that is stout and very short. Underneath the rhizome, it has thick and swollen roots.
It has numerous leaves, that are typical iris-looking leaves, that are similar in form to a bearded iris, except fan shaped. They are also similar to a Vanda orchid's leaves. They grow from the base of rhizome (i.e. basal) and are sword-shaped, greyish green and slightly curved. The leaves have no midvein and can grow between long and wide.
It has dichotomously, or multi-branched stems, which can grow up to between tall. The tall stems keep the flowers much higher than the foliage of the leaves, and they have 4 or 5 leafy spathes (leaves of the flower bud), which are green, lanceolate (spear-like) shaped and long.
It blooms in the US between May and midsummer. Elsewhere, it begins to bloom in summer, or late summer, between July and early August.
It unusually blooms in the late afternoon, at approx. 3 o'clock, or 4 o’clock. This occurs at the time of hearing ‘’Vespers’’, hence its common name, of ‘Vespers Iris’. They fully open out in just a couple of minutes, but only last one day, as they twist into tight little spirals after dark and then drop from the stem. Withered flowers are never normally seen on the stems.
Each stem can hold between 3–6 flowers. This means, a well established plant can have nearly hundreds of flowers, the display of flowers can last for up to 3 – 4 weeks. The flowers are fragrant. As the flowers (and nectar) are extremely attractive to hummingbirds and honeybees, cross-pollination can take place and then later seeds can be formed.
Unfortunately, the flowers are small, at about long.
They come in various shades from violet, mauve to purple, purple, lavender, pale blue, white, (rarely), cream, or pink.
Like other irises, it has 2 pairs of petals, 3 large sepals (outer petals), known as the 'falls' and 3 inner, smaller petals (or tepals), known as the 'standards'.
The outer petals are broadly oblanceolate shaped (much longer than wide and with the widest portion near the tip), long and about 1 cm wide. The ‘claw’ (section closest to the centre) is striped, or reticulated (marked with a grid), with yellowish brown and the limb (the end part) has darker spots on a central, pale patch. The patch can have a whitish colour tinged with green and the spots can be lilac-mauve, brown-purple, or red-purple. The tips of the falls are free from any spots or markings. The plain inner petals are narrowly obovate shaped (teardrop-like), long and 6–8 mm wide, with a retuse apex (rounded end with a depression).
It has very distinct arms on the flower style, which are long, with purplish brown markings.
Its perianth tube is extremely short, or missing. It has stamens that are long and a green ovary that is 1 cm long.
After it has flowered, the plant will produce a seed capsule and seeds, between August and September.
The seed capsule is cylindric in shape, yellowish-green and long and wide. Inside, it has elongated, or elliptic shaped, and dark brown, or brown coloured seeds, that have small wings. As compared to Iris domestica and related hybrids which have large round black seeds.
Genetics
As most irises are diploid, having two sets of chromosomes. This can be used to identify hybrids and classification of groupings. It has a chromosome count of 2n=32. It was counted three times; Doronkin, V. M. & A. A. Krasnikov. 1984. "Cytotaxonomic studies in some Siberian species of the genus Iris (Iridaceae)". Bot. Zhurn. SSSR 65 (5): 683–685. (In Russian). Sha, W., L. h. Wang, X. j. Yang, X. l. Qi, G. h. Ma & D. y. Zhao. 1995. "Chromosome numbers of 20 species from north-east China". J. Wuhan Bot. Res. 32 (2): 180–182. Yan, G. x., S. z. Zheng, F. h. Xue, J. f. Yun, L. y. Wang & X. q. Fu. 1995. "The chromosome numbers of 35 forage species and their geographical distribution". Grassl. China 1995 (1): 16–20.
Biochemistry
The rhizome of Iris dichotoma Pall., contains isoflavonoids as the main bioactive compound.