#dimorphotheca

This weeks microscopy features Dimorphotheca (Osterospermum) ecklonis (Asteraceae)! This is a non-native species of daisy from South Africa that’s commonly grown in gardens here in Aus. Their ligules (what appear as petals) can be white to purple, while the centre disc florets are a deep blue/purple. They’re quite striking flowers up close! The contrast of the deep yellow pollen with the blue/purple florets is stunning.

BUT lets do a brief dive into daisy flowers because they're not actually 'flowers', they're inflorescences made up of hundreds of little florets (mini flowers!).

Daisies can be made up of one or both types of florets- ligulate (ray) and disc. Ligulate florets are what we think of as the petals of the daisy inflorescence. They have zygomorphic symmetry (being only symmetrical if you slice it down one plane). The ligules soft, fleshy and very showy. They can be bisexual but are more often female or completely sterile. In this photo you can juuust see the inner flower parts on the upper right ligulate floret. For this species of daisy ligulate florets ocurr in a singular ring around the outside of the inflorescence, with disc florets occur inside.

Disc (ray) florets look much more like mini flowers. They're actinomorphic (symmetrical from any plane you cut it) with five petals and a central pillar of sex organs. They're most often bisexual. This is a close-up of one here. The yellow stuff is pollen being pushed out of the central pillar (which is a ring of anthers, the dark parts under the pollen) by the stigma (female part).

Daisies have a thing called secondary pollen presentation, where pollen is deposited on the stigma, the stigma displays the pollen for collection by a pollinator and then becomes receptive to recieve donor pollen once its own (self) pollen is gone! Unfortinetly I don't have any photos of this species that far along in its development, so you'll have to settle for seeing it in Olearia lirata. The stigma are the two topmost bits sticking out of the ring of anthers (orange coloured organs).

And here's that pollen at a much higher magnification. Daisy pollen is sphericle and covered in what look like spikes (they're echinate, prickly). This lets them stick to pollinators and floral visitors better for transport to the next flower! I can't get that level of detail with this setup, but maybe I'll take a photo with a compound microscope and share that at some point.