Flowering of Scabiosa caucasia (Caucasian scabious)
A detailed photographic study of floral development
The Caucasian scabious is a beautiful multi-floreted flower that has a fascinating form of floral development. The early flower undergoes a very specific sequence of floret opening for example. The outer florets open first followed by the second-most outer ring. The inner-most buds then open leaving temporarily creating a ring of unopened buds. In other words, there is a very precise pattern of development. Is there a reproductive advantage to the flower of having large outer petals that are also of a different colour? If you go to the photo gallery showing insect visitors you will be able to see that pollinating insects land on those large outer petals.
Caucasian scabious is sometimes known by the name ‘ladies pincushion’. This is due to the fact that after the anthers have been shed and the filaments of the stamens have withered the carpels (pistils) grow longer and resemble the pattern of sewing needles in a pincushion.
A range of sequential floral development stages is indicated by the red letters. These are explained and illustrated in detail later. Flowers marked B show the beginning of enlargement of the outer florets. C shows the beginning of pigmentation in the outer florets. In D the outer rings of florets have opened. In E all of the florets are open the anthers have been shed and the carpels are extending. The asynchrony of flower development is clearly shown.
During early development, this flower does not seem to be at all interesting when examined at a distance. However, when examined in closeup there are intriguing accessory structures around each flower bud. There are long filamentous structures called pappus bristles and hairy green triangular looking green structures called phyllaries (singular phyllary). The pappus bristles have an important function in the formation of the fruiting body, which will be illustrated at the end of this account. In early flower development, I speculate that they might have another function in early development such as playing a part in flower organisation and also and offering some form of protection. The phyllary is a modified leaf (or bract). Clearly, they could also play a protective function since the hairs that emerge from them are quite extensive.