Not Yet Native of the Week: Strawflower

Waspy interest in this Australian flower

I had trouble deciding if this was my inaugural Wasp Wednesday or an Australian of the Week, but I haven't been keeping up with the NYN of the Week, so behold Helichrysum bracteatum, the Australian Strawflower, Golden Everlasting, or Paper Daisy. Well, actually, if you check on the USDA website you will find it called Bracteantha bracteata the Bracted Strawflower, which seems a bit of a bract overkill, and if you check the more recent botanical literature it is called Xerochrysum bracteatum.

Golden in the wild, but a rainbow in cultivation

If you've grown strawflowers, then the Golden part of Golden Everlasting may not make much sense, but in the Australian bush the flowers in this complex of species are often yellow (some are white). It would be interesting to see if the colour range in cultivation is being maintained where Strawflower is naturalized in Connecticut and Massachusetts. However, the 'everlasting', 'paper daisy', and all the bract-formations all come from what look like petals, but are actually colourful bracts that when dry make quite nice dried 'flowers'.

Flaming bracts and a ring of golden florets

Like all members of the Asteraceae (aka Compositae), the apparent flower is actually a composite head of mostly tiny florets that each produce pollen and, if lucky, a seed (aka achene). Unlike may composites, the brightly coloured rim of the Strawflower head is not composed of ray flowers, but of sterile, and usually more leaf-like structures called bracts.

Bract-licking Western Yellowjacket

The petal-like bracts, and also the leaves directly under the bracts, on Strawflowers secrete nectar. Nectaries outside of flowers (and remember the true flowers here are tiny and enclosed by the bracts) are called, logically enough, extrafloral nectaries. Nectaries that surround a flower or cluster of flowers are thought to attract natural enemies of the things that like to eat seeds and often the bract-licking insects attracted are ants.

Black ants feasting at peony bracts

 Ants are attracted to Strawflower nectaries, apparently too commonly for us to have thought it worth a picture, but it is questionable how much they help the Strawflower set seed. O'Dowd & Catchpole (1983*) tested this hypothesis in Australia, but although fewer insects were present when ants were around, there was no effect on seed set. It seems unlikely that Strawflowers are simply being generous with their nectar, but perhaps any benefits vary from year to year. In Alberta, Strawflower is an annual, although it sometimes comes back from seed. In Australia, Strawflowers are usually perennials, so they tend to have more than one chance to set seed. But science is very strict about hypotheses: fail the test and the hypothesis should be summarily executed (well, in theory, anyway).

Whatever their function may be, hornets approve of extrafloral nectaries on Strawflowers

*O’Dowd DJ & EA Catchpole. 1983. Ants and extrafloral nectaries: no evidence for plant protection in Helichrysum spp. – ant interactions. Oecologia 59: 191-200.