Mulberry

Mulberry is easy to grow and hard to name, and the second half is why this file is shorter than the crop’s popularity would suggest.

The species boundaries are genuinely blurred, and not only in catalogues. Morus alba was brought to North America in the colonial period to support a silk industry that never took hold. It naturalised, spread past the range of the native M. rubra, and hybridises with it. Research describes asymmetrical introgression and treats the genetic integrity of red mulberry as threatened — the native species is being absorbed rather than simply outcompeted. Recent work has gone to chloroplast genomes and species-specific molecular markers precisely because morphology cannot reliably separate pure M. rubra from hybrids.

That has a design consequence worth stating plainly. Most of the good fruiting cultivars below are alba × rubra hybrids. Planting one is planting a pollen source that can hybridise with any remnant native red mulberry in range. In most settings that is unremarkable; near a known M. rubra population it is a decision, and it should be made on purpose rather than by default.

The naming problem follows from the biology. Cultivars are sold under conflicting species attributions — the same plant listed as M. alba, as M. alba × rubra, and as M. macroura by different nurseries — and at least one documented case of cultivars being sold under each other’s names. Where the sources disagree, the records below say so instead of picking a side. Treat a species name on a mulberry tag as the nursery’s best guess.

The rights are simple by comparison. Almost everything here is a chance seedling somebody noticed, most of them before modern plant variety protection, and freely propagated. Mulberry roots and grafts readily, which is part of why the cultivars spread widely and why their identities drifted along the way.