Who Can Cross With Whom?
Rhododendron ABC's #3
In our first two 'Rhododendron ABCs' we discussed the concepts of species and hybrids. It is about time to turn our attention to rhododendron classification and grouping. We have learned that species generally produce offspring that are like the parents and when two separate species are crossed to produce hybrids, the offspring win have traits with considerable variation. We have also learned that rhododendrons are among the plants whose hybrids are fertile and can be used to produce even more complex hybrids than the first generation crosses so that the number of possible hybrids with widely varying traits is large.
This ability to produce hybrids by means of inter-specific crosses is noteworthy, but it does not, however, mean that it impossible to cross any species in the genus with any and every other species.
As with all creatures, there is a requirement for a least some compatibility of traits in the parents in order for viable offspring to be produced. Relationships are determined by the study of characteristics of individuality collected plant specimens.
Among the characteristics used are:
1. the morphological nature,i.e., structure of stems, leaves, etc.
2. flower form and color,
3. shape, type and number of reproductive organs in the flower,
4. type of seed capsules,
5. blooming time,
7. size of mature plant.
These are just some of the things that are studied. But there are more, and the classification and determining relationships is a whole subject in itself called Taxonomy (fromthe Greek, taxus, meaning arrangement and nomos, meaning law.
Owing to the fact that rhododendrons are widely distributed throughout the whole northern hemisphere, and have adapted themselves to many different locations and climates, they have differentiated into a very large number of species. Some authorities (known as splitters) put the number as high as 1,200 and others (known as lumpers) say there are less, perhaps as low as 700. In any case, the genus Rhododendroncontains a very large number of broadly related species. This complex and diverse group has caused all sorts of problems to taxonomists-- just who is related to whom?
After many years of study and, in some cases controversy, we all can agree
on four somewhat arbitrary subdivisions of the genus. These are:
1. Lepidotes - those with scaly leaves,
2. Elipidotes- those without scales on the leaves,
3. Azaleas- you just have to know them when you see them, but there are two sub-types of these: deciduous azaleas that drop their leaves every year and evergreen azaleas that don't.
4. Vireyas- generally tender tropical plants of warm localities.
Within these broad, and generally related groupings (but rather distantly related), we can say that species within each group can hybridizewith other species in the same group, but have much difficulty (but it is not impossible) in hybridizing with species in the other groups. We shall discuss later, in more detail, how taxonomists have come to grips with the wide variability of the species in the genus rhododendron.
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