More petals often equals more appeal for flower lovers. Double and semi-double blooms are popular among gardeners for their lush, ornate appearance. But, while they are common in cultivated varieties, they are exceptionally rare in the wild.
So, when researchers from China discovered a new species with naturally occurring semi-double flowers, they knew they had found something special.
What are single, semi-double, and double flowers?
To appreciate this discovery, it’s helpful to understand what makes a flower “single,” “double,” or “semi-double.”
- Single flowers have the typical number of petals for their species, arranged in a single row. This number is usually five in the rose family (Rosaceae). Single-flowered plants are by far the most common wild species.
- Double flowers have been bred or mutated to have many extra petals, often replacing stamens, giving them a full, layered look. While they are popular for their aesthetic value, double flowers are often poor (or entirely useless) for pollinators.
- Semi-double flowers are an intermediate form. They have more than the typical number of petals (often in two whorls), but fewer than fully double flowers, usually around 10–12 petals. Semi-double flowers are rare in the wild and – like double flowers – are almost always cultivated.
Double and semi-double blooms are prized for their beauty and prolonged flowering, but are typically only seen in cultivated ornamentals, not in wild populations.
Rubus semiplenus
Discovered in 2022 during a botanical expedition in Hunan Province’s Nanyue Hengshan National Nature Reserve, Rubus semiplenus is a rare example of a wild species with semi-double flowers. Scientists from Yunnan University and local botanical institutions confirmed it as a new species and published their findings in the open-access journal PhytoKeys.
Unlike most of its Rubus relatives, R. semiplenus grows as a small herb or dwarf subshrub rather than a woody shrub. The bramble’s leaves are simple and nearly round, which is also unusual for the genus, and its flowers have 10–12 white petals arranged in two whorls, clearly distinguishing it from related species like Rubus hirsutus, which has the typical five-petaled, single flowers.
The floral trait seen in R. semiplenus is exceptionally rare in wild Rubus species. While some cultivated varieties and a few exceptions (like Rubus rosifolius var. coronarius) show similar traits, spontaneous semi-double flowers are almost unheard of in the wild. The discovery is also taxonomically significant. Genetic and morphological analyses place R. semiplenus within the section Rosaefolii, but it is the only known member of that group with both simple leaves and semi-double flowers, which may provide insight into floral evolution and development within the Rubus genus.
Original source
Wang T-T, Li M-H, Kuang D-Y, Xia J-L, Wang Q-P, Wang H-C (2025) Rubus semiplenus (Rosaceae), a new species with naturally occurring semi-double flowers from Hunan, China. PhytoKeys 257: 79-93. https://doi.org/10.3897/phytokeys.257.150519