Hybrids between Elepidote and Lepidote Rhododendrons
Research Station for Arboriculture at Boskoop
During the last few years many different crosses have been made between elepidote and lepidote rhododendron species or hybrids at the Research Station for Arboriculture at Boskoop, as part of the breeding work in Rhododendron. This may be a means to find new and interesting hybrids.
Since Dr. J. M. Cowan reported about the hybrid R. 'Grierdal' (The Rhododendron Year Book of the Royal Horticultural Society, London 1946: 48-54) which certainly is a hybrid obtained by crossing of the elepidote R. griersonianum with the lepidote R. dalhousiae, no further evidence is given in literature about comparable crossings.
At Boskoop, however, in crossing elepidote and lepidote rhododendrons in some cases a progeny was obtained and a few plants resulting from two crosses, carried out in 1967, flowered in the spring of 1969.
The seeds were harvested at the end of September 1967 and were sown in November of that same year. During wintertime the plants were grown in a greenhouse under strong artificial light. From the end of May until the end of September 1968 the plants were outside in a frame, under shelter, and during the following winter again in a greenhouse under strong artificial light. As a result of this treatment flowering was accelerated and a few plants were already flowering in June or July 1969. After such a short growing period, the plants were still rather small at the time of flowering and only a few flowers were formed.
In both cases it is highly probable that these plants are really hybrids, and it is interesting to observe that the shape of the scales on the leaves resemble those of R. 'Grierdal', clearly described in literature. The scales consist of a stalk and a rounded head, whereas the scales of the lepidote parents have a short stalk and a shield.
Fig. 27. R. 'Metternianum' x
Fig. 28. R. dauricum x
In crossing R. 'Metternianum' (R. metternichii var. kyomaruense) with R. pemakoense, elepidote x lepidote, many plants were obtained. Most of the progeny, however, show a strong resemblance to R. 'Metternianum', the seed parent, and probably are of apomictic nature. Only a few plants were clearly different: smaller, with small leaves and with scales. Three of these looked very similar and did already produce flowers. At the time of flowering these plants were about 15 cm in height. The flowers are funnel shaped, about 3.5 cm in diameter, having a very pale lilac-pink colour. On the young leaves, scales are to be found on both the upper and under surface with a few hairs on the upper surface. On the older leaves scales are observed only on the under surface. This proves the assumption that it is a cross between the elepidote seed parent and the lepidote pollen parent, since the hybrid is a lepidote.
The other cross from which only one plant flowered, is a cross between the lepidote R. dauricum (white form) as seed parent and the elepidote R. 'Elizabeth' as pollen parent. In this case too many plants were obtained, but during the raising period one after the other died, leaving only a few. The only flowering plant is of an erect type, at the time of flowering about 20 cm high. The flowers are funnel shaped, lilac pink (MCC: Solferino Purple 26/2). On the young leaves scales and a few hairs are to be found on the upper and under surface, whereas on the older leaves scales are observed only on the under surface.
In this case, the lepidote being the seed parent, it is interesting to note that the shape of the scales on the leaves resembles those of the above mentioned hybrids. Comparing them with the lepidote parents, the number of scales on the leaves of the hybrids is reduced. It is too early yet to give an exact description of the characters of the hybrids since the plants are still rather small and only flowered once.
As mentioned above, many different combinations of elepidote and lepidote crosses are tried, and only in a few cases seeds were obtained. However, a part of the progeny of certain crosses consists of very small and chlorotic plants which died at an early stage, which, as yet, can not be explained.
Summarizing it can be said that the common assumption that lepidote and elepidote Rhododendrons cannot be crossed, can no longer be sustained.