Several methods have been used to define Hyacinthoides as a distinct group. Studies in the 1930s of their morphological features found that Hyacinthoides all feature long, paired floral bracts. They also have coalescent bulb scales which are completely renewed each year.
Since then, DNA studies have been used to show that these plants all share a common ancestry.
Taxonomists used to think there were two distinct groups of Hyacinthoides:
- Hyacinthoides - these species have bell-shaped flowers and the stamens are fused to the tepals to some extent. Hyacinthoides hispanica, the Spanish bluebell, and Hycinthoides non-scripta, the native UK bluebell, both belong to this group.
- Somera - these species have open flowers and the stamens are only attached at their base to the tepals.
However, a new species called Hyacinthoides paivae was found in North west Iberia in 1996 and it displayed characteristics of both groups. This discovery suggested that the division was incorrect. DNA studies at the Museum also suggest this.
Scientists at the Museum now think there may be three distinct groups of bluebell species, reflecting their geographical distribution:
- Hyacinthoides italica, Hyacinthoides aristidis, Hyacinthoides ciliolata, and Hyacinthoides lingulata - these plants mostly flower in the autumn and winter. They grow in North Africa, Southern France and Northern Italy.
- Hyacinthoides flahaultiana, Hyacinthoides mauritanica, Hyacinthoides reverchonii - these plants flower in the spring. They grow in North Africa and Southern Iberia.
- Hyacinthoides cedretorum, Hyacinthoides hispanica, Hyacinthoides non-scripta, Hyacinthoides paivae - these plants flower in the spring. They grow in Western Europe and the North African mountains.