Indigofera
Floral Committee B (now called the Woody Plant Committee) held a meeting at RHS Garden Hyde Hall on 29 June 2004 concentrating on the genus Indigofera.
Samples of flowering material of the genus were brought from a number of sources, including Committee members, and these remained on display for the public after the meeting.
Dr Brian Schrire gave a very comprehensive survey of the genus starting with its position within the family and within the tribe Indigoferae. He explained how DNA sequencing could be used to work out the relationships between genera and species.
Indigofera is a pantropical genus of around 700 species which separates into four major groups. Although the majority would not be hardy in the UK, there are about 12 species could be grown outdoors in Britain and there are almost certainly other species in the wild which could also be hardy. Most of those in cultivation are from China and the Himalayan regions.
Dr Schrire described each of these hardy species, emphasising the distinctive characters and Ms Susyn Andrews added details of their distribution and the history of their introduction. The plant material contributed by Committee members was checked and used to illustrate the presentation.
The following species are those found most frequently in cultivation in the UK.
| I. ambylantha | Rather small erect racemes of pink flowers. Leaves with many leaflets and a very long terminal leaflet. A very hardy and vigorous plant. |
| I. decora (syn I. incarnata) | Similar to I. kirilkowii but more tender and with narrower leaflets. |
| I. decora f. alba | Flowers white, slightly more hardy. |
| I. hebepetala | Erect racemes of deep wine red flowers. Leaves with large leaflets with the terminal leaflet much larger than the rest. The most recently introduced species. |
| I. heterantha (syn. I. gerardiana) | Erect racemes of bright magenta flowers, the wings brighter than the standard. Leaves ash/blue grey with many leaflets. The hardiest species and the most widely cultivated. |
| I. himalayensis | Plants grown in gardens as I. dielsiana or I. balfouriana are usually this species. Short erect racemes of clear bright pink flowers. Leaflets more or less glabrous. The earliest species to flower and reliably hardy. |
| I. kirikowii | Pendulous racemes of very large bright pink flowers. Leaves with broad oval leaflets. |
| I. pendula | Long pendulous racemes which can reach to 60cm (2ft) in length. Flowers two-toned with rose-purple standard with ash grey-back, and paler wings. Leaves with narrow elliptic leaflets. Less hardy than some species but once established usually recovers if hit by a cold winter. |
| I. potaninii | Most plants under this name are wrongly labelled and there are few correctly named plants in gardens. Racemes held sideways with coral red flowers. |
| I. pseudotinctoria | Rather small erect racemes of late flowering pale pink flowers and a low growing habit. ‘Rose Carpet’ is a prostrate cultivar seen by the speaker in the USA. |
| Some of the less common and less hardy species include: | |
| I. australis | Upright racemes and blue grey foliage. Introduced on a number of occasions but not reliably hardy. |
| I. jucunda | A South African species with pink and white flowers suitable for a conservatory. |
| I. venulosa | A tender species possibly related to I. decora and what may have been cultivated in the past as I. decora f. rosea. No plants now known in the UK. |
| A number of other species have also been collected recently and are in the gardens of one or two plant collectors. These may prove to be hardy and become useful garden plants in the future. | |
| I. hancockii | A species with dark brown flower buds and many leaflets. Related to I. heterantha. |
| I. henryi | A species with many leaflets and flowers on long pedicels. |
| I. szechuanensis | Small racemes of deep pink-purple flowers and very dark buds. Leaves with few leaflets and plant with a tangled habit. |