User:Saxifraga

''Rodgersia' The genus Rodgersia was created by an American taxonomist,A.Gray, in 1885.Gray named it after the US Admiral, John Rodgers, who commanded the expedition in which R.podophylla was discovered in the 1850's.It is included in the Saxifragaceae. R.podophylla was the type species.

Since the review of the genus it has included five species. R.podophylla, R.aesculifolia, R.sambucifolia, R.pinnata  and R.nepalensis. Pan Jin-tang decribed several varieties R.aesculifolia var. aesculifolia, R.aesculifolia var.henrici (Franchet) C.Y.Wu, R.sambucifolia Hemsl.var. estrigosa J.T.Pan, R.pinnata Franch.var.pinnata and R.pinnata var.strigosa J.T.Pan.

R.podophylla is native to Japan (the island of Honshu) and to Korea. All the other species are found in China, including Tibet, and Nepal. The geographical ranges of all but R.nepalensis overlap each other.

In their native habitats they grow by streams and in shady moist woodland. In cultivation they thrive in soil that never dries out but is not waterlogged. They will grow in sun under these conditions in good humus rich soil but they are susceptible to sun- and wind-scorch. They are hardy down to Zone 5 but their new growths in the spring can be damaged by late frosts.

The thick rhizomes spread just under surface of the soil. Three of the species are clump forming whereas R.nepalensis and some forms of R.podophylla can cover large areas quite quickly once they are happily established.

The strong leaf stems grow to an average height of about one metre but this depends on the variety & growing conditions. The spread of the compound leaves, especially of R.podophylla can also be up to one metre making them architectural plants in cultivation. The flowering stems rise above the foliage and the panicles of flowers, although lacking true petals, are spectacular and colourful being white, cream, pink or red except in  R.nepalensis which are greeny yellow.

The leaves of many varieties are attractive in the Spring when, grown in good light, they have a bronze or copper hue.This is especially beautiful in the Purdomi group of R.aesculifolia which keep a metallic sheen into early summer. In the autumn(fall), the leaves turn attractive shades of coppery-brown. The seed heads are also attractive, those of many R.pinnata are claret coloured which deepens as winter progresses.

Discovery of the Genus.

As mentioned at the begining of this article,R.podophylla was discovered in the 1850's when it was brought back from Japan to the US. By 1871,it was flowering in the Imperial Botanical Garden at St. Petersburgh and in 1878, seed brought back to a British nursery, Veitch & Sons, produced flowering plants.

R.aesculifolia was discovered by Abbe, later Pere, David in 1869.

The third species R.henrici was initially thought to be an astilbe & was collected by Prince Henri d'Orleans in 1895. This has recently been reduced to a varietas of R.aesculifolia.

The fourth species, R.pinnata was also discovered by Abbe David, in China's Yunnan province, in 1883. It first flowered in the UK in 1902.

The fifth species, R.sambucifolia was discovered by Ernest Wilson 1904 in Yalung, China.

The last species to be discovered was R.nepalensis collected by Peter Schilling, UK, in 1966 who made a second collection of seeds of this species. There are distinct differences between the plants raised from these two collections whose numbers are EMAK 713/901 and ED2879.

In older literature there is mention of R.purdomii named after William Purdom who collected in China in around 1910. The herbarium specimen of a plant raised from that seed, at Kew, identifies it as R.aesculifolia. More of this under the description of R.aesculifolia.

The Species.

R.podophylla Gray (diploid 2n=30)

The leaves of this species are palmate. The individual leaflets, from 5 to 7 in number, have between 3 to 5 "drip tips", angular terminations which give the impression of a duck's webbed foot! This is sufficient to identify R.podophylla from all the other species. There are two forms of R.podophylla, one which has tough leathery leaves which are often bronze in the spring & autumn, & a thinner leaved form which remains a light green colour. R.podophylla is often very shy at flowering, but can cover large areas by means of its spreading rhizomes. The flowers are white, the sepals ageing to green as do the ovaries.

R.aesculifolia Batalin (tetraploid 2n=60")

The leaves are symmetrically palmate radiating from a central point most often without petioles.They are obvate with acute apices and coarsely serrated. Recently, R.aesculifolia has been divided into three distinct taxa.

1)White flowered.

This has small flowers, 2 - 8mm in diameter. The green, white or yellowish buds open to white flowers that go green with age. It has green leaves throughout the growing season & airy inflorescences with curled flower clusters.

2)Purdomii taxon.

This also has small flowers 2 - 8mm in diameter but the flower buds are pink opening to sepals tinged or tipped pink turning white, the flowers ageing green. The young leaves are copper or bronze in colour & the older leaves retain a metallic shean. The inflorescences have an airy appearance as in taxon 1.

3) Henrici taxon.

This has large flowers 8 - 18mm in diameter, a major difference with the other two taxa. The bright pink sepals and ovaries get progressively deeper in colour as they age & remain claret-coloured through autumn.

The inflorescences have nothing "airy" about them but are solid-looking, broad based with flower clusters that have almost flat tops with their undersides clearly visible when viewed from the side. They form tiers as in a multiple wedding cake & the flowers are closely packed along the pedicels.

The texture of the leaf surface of var. henrici is firm and there is no tendency to deflect downwards from the mid-vein or at the apex, as in the soft-textured var. aesculifolia. All the veins in var. henrici are sunken, giving the top surface of the leaflets a quilted effect and on the underside, all the veins are prominent.

The leaflets of var.aesculifolia have an almost smooth upper surface and only the main veins are prominent on the underside. The normal number of leaflets for var. henrici is 7 - 9 ; for var. aesculifolia it is 6 - 7.

Pan (1994) provides a key that seperates R.aesculifolia var. aesculifolia from var. henrici. This key states that var. henrici has more glandular hairs on the ventral surface of its sepals than var. aesculifolia and that the arcuate (curved) sepal veins meet at the tips whereas they do not in var. aesculifolia.

From a gardeners point of view, the general differences in the non-microscopic features of the plants are sufficiently diagnostic.

R.sambucifolia Hemsley (tetraploid 2n=60)

The leaves are pinnate and remain green throughout their life. The number of pairs of leaflets varies with the age of the plant and habitat. It is the smallest, in statue, of all of the species having foliage and flower spikes around 500mm tall. The small white flowers rapidly age to browny green. The two varieties established by Pan are distinguished by microscopic features.

R.pinnata Franchet (tetraploid 2n=60)

This species has the most diverse leaf form of any of the Rodgersia and this leads to mis-identification and labelling in horticulture. Rarely are the leaflets arranged in true pinnate form with evenly spaced leaflets.They vary from pseudo-pinnate, when the leaflets can be bunched 2 to 5 at the petiole and 3 at the apex with varying numbers of pairs of leaflets between with varying lengths of rachis, to plants where the rachis is so compressed as to need very close inspection to ascertain that it is not palmate. The size of the individual obovate-lanceolate leaflets ranges from 20mm long x 10mm wide to double those measurements depending on variety and growing conditions. The height of the leaves may exceed one metre and that of the inflorescence, one and a half metres. The flowers can be white, palest pink to deep claret colour and the subsequent seeds heads range from green through to deep mahogany. There are many cultivars, R.pinnata is very variable in all its aspects and readily hybridises with both R.podophylla and R.aesculifolia. As with R.sambucifolia, the two varieties established by Pan are distinguished by microscopic features.

R.nepalensis T.A.Cope ex Cullen

This has a truly pinnate leaf, blue-green in EMAK 713, yellowy-green in ED2879. The individual leaflet are about 15mm long and 5mm wide with markedly serrated edges, tipped red brown in EMAK, yellow in ED. The sepals of EMAK are pale green, those of ED pale yellow. The flower colour distinguishes R.nepalensis from all other Rodgersia