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Updated: May 16, 2025
It is very interesting to compare old botanical books, or even old drawings and engravings containing figures of anomalous plants. Sebastian in a flower-garden. Of the plants many are clearly recognizable, and among others there is one of the "one-leaved" variety of the strawberry, which may still be met with in botanical gardens.
The "one-leaved" strawberry has already been referred to. It originated from the ordinary type in Norway and at Paris. The walnut likewise, has its monophyllous variety. It was mentioned for the first time as a cultivated tree about 1864, but its origin is unknown.
According to Smith and to Loudon, the "one-leaved" ashes are found wild in different districts in-England. Intermediate forms have not been recorded from these localities. This mode of origin is that already detailed for the laciniate varieties of alders and so many other trees.
As far as I have been able to ascertain, these are produced on weak twigs under unfavorable conditions; the size of the terminal leaflet decreases and the number of the lateral blades increases, showing thereby the presence of the original pinnate type in a latent condition. The sudden origin of this "one-leaved" acacia in a nursery may be taken as a prototype of the ancient origin of Desmodium.
If the leaves are sessile, the analogy with the teasels is complete, as shown, for instance, in a case of Cotyledon, a crassulaceous plant which is known to produce such cups from time to time. They are narrower than those of the teasel, but this depends, as we have seen for the "one-leaved" ascidium, on the shape of the original leaf.
The difference is so striking and affords such a reliable feature that Koch proposed to make two distinct varieties of them, calling the pure type Fraxinus excelsior monophylla, and the varying trees F. excelsior exheterophylla. Some writers, and among them Willdenow, have preferred to separate the "one-leaved" forms from the species, and to call them Fraxinus simplicifolia.
Only very few instances have been described, and are cultivated in gardens. The ashes and the bastard-acacia may be quoted among trees, and the "one-leaved" strawberry among herbs. Here it seems that several leaflets have been combined into one, since this one is, as a rule, much larger than the terminal leaflet of an ordinary leaf of the same species.
Hence it may be assumed that the "one-leaved" ashes have sprung suddenly but frequently from the original pinnate species. The pure type of Willdenow should, in this case, be considered as due to a slightly different mutation, perhaps as a pure retrograde variety, while the varying strains may only be eversporting forms. This would likewise explain part of their observed inconstancy.
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