It is not purely Mendelian, because it doesn’t appear to be one gene that affects the shape of the orchids. There seem to be many genes involved, with variations in the outcome.
The genetic base of the shape of orchid is very complex.
Mendelian traits are described as simple traits determined by one gene. The different alleles of the gene contribute to the difference in the trait. This is true for some traits in plants, animals including humans and other organisms, but not for the shape of orchids.
The shape of orchid flowers is determined by the ABCDE group of genes that are responsible for the body plan in plants. These genes are the equivalent of HOX genes of animals.
The protein products of different genes of the ABCDE group interact with each other in complex ways creating different shapes of orchids.
