Sometimes rose seeds contain two embryos. I don’t see it very often; perhaps 1 in 1000 germinations give twins. I’ve never seen triplets. This press release describes how scientists at the University of California, Riverside, induced twin and triplet seedlings by increasing the level of Vitamin C in plant ovaries. They used tobacco plants, but said, “Because the early stages of embryo development are so conserved among plant species, we expect that vitamin C will have a similar effect in almost any plant”
I wonder whether vitamin C in solution would work as well, for those of us who are fresh out of DHAR.
I have read about multiple-embryo seeds occurring occasionally in some distant hybrids. Bradley (1906) wrote, “Calostemma luteum x Pancratium maritimum gave a quantity of fertile seed, and the seedlings are growing strongly, but none have flowered yet, so it is uncertain if the cross has taken. Curiously, several of the seeds developed two plants, and one seed gave three plants from the one seed.”