I tried looking for information on this yesterday, but all I got were dozens of articles explaining the differences between mulberries and blackberries. Well, one could say that the need for those articles reflects the observed situation that the fruits of these two unrelated plants look very similar. Of course, the plants themselves do not resemble each other in any way; but I can give the benefit of the doubt and say that the articles were hopefully directed toward people who are familiar only with the fruits and not the whole plants.
Anyway, it does seem curious to me that here we have a genus in the Rosaceae (Rubus) and one in the Moraceae (Morus), morphologically very different in habitus, foliage, flowers, and armament, and to all appearances occupying different niches, yet with fruits so similar to each other and so different from those of their relatives (i.e. apples, rose hips, and peaches in the Rosaceae; figs in the Moraceae).
In some ways, these can be seen as modifications on related fruits. Strawberries (Rosaceae) could be viewed as having the same underlying structure as blackberries, i.e., an aggregate fruit; and in the Moraceae, noni and breadfruit are also aggregates. Still, a mulberry looks more like a blackberry than like a noni or breadfruit, and a blackberry looks more like a mulberry than like a strawberry.
But if these are an example of convergence, what would be the mechanism or selective pressure? And how would it operate across different niches to affect only the fruits and not the whole plants?
the briefest way I can think to answer this is that both of them come from lineages of plants with animal-dispersed fruits (specifically endozoochorous seed dispersal), both happen to have had an underlying infructescence involving numerous carpels on a central axis, and both have developed the strategy of packing together multiple individual fruits/seeds together rather than separately in order to disperse them simultaneously.
beyond that, I doubt there is any very specific thing tying these two together. out of thousands of plant genera with different types of fruit, it’s not surprising that a couple (or more) would end up looking similar to humans, especially if they happen to have a similar morphological substrate and dispersal strategy. and who knows if they look similar to any other animal!
FWIW, there is also Iris domestica, the “Blackberry Lily” (Iridaceae), which has some visual resemblance albeit with a lot fewer fruits in a capsule. I’m not sure whether those fruits are adapted for animal consumption and dispersal.
are we discounting cultivation by general hominids by occam’s razor around this forum? i dont find it all that specualative, although i wouldn’t want to try to back it up
I’m not sure how convergence is defined, but it certainly looks like one! They are, though, different kinds of fruits: the mulberry is a multiple fruit (each fruit in a cluster is from a separate flower) while the blackberry is an aggregate of drupelets.
The word “morus” and cognates have been passed back and forth by the two kinds of plants, so it’s hard to determine which it originally meant.
My two cents worth here.
I would say this is a case of convergent evolution. Dolphins, tuna and sharks all have the same body plan but are from very different linages. It would seem that a body with a tail fins, and a dorsal fin on a streamlined body, is the most efficient model for travelling and hunting in the open ocean.
Mulberries and blackberries, along with all other fruit bearing plants, produce edible fruits as a means of seed dispersal. Blackberries and mulberries both originated in the Northern Temperate Zone, so it is likely the same or similar species of birds fed on both of them and dispersed the seeds. I guess the these two fruits are the optimum size, flavour and structure to appeal to birds.
good point about the fruit arrangement – I should have been more clear. the inside of a mulberry is considerably more complicated than the “simple” blackberry drupecetum. I guess it’s comparable to a fig.
Figs and mulberries are in the same family. “Sycomore” is from the Greek words for the two stuck together. Then there’s Dorstenia, which in Lojban is called “karfigre” (open fig) because it looks like a syconium opened up.
What’s also crazy is Suhosine Mulberry (Debregeasia edulis) has edible fruits that look like Orange Mulberries and is part of the Urticaceae family (which is Phylogenically sister to Moraceae Family).
