Tuesday, 1 March 2016

Girls who are boys, a botanical blur


"Girls who are boys..."

The Brit-pop-indie band Blur went on to sing about girls who like boys to be girls, and so on. It's from a song (Girls & Boys) written in the 1990s, in response to the rampant promiscuity observed at one of those European island holiday resorts.

Promiscuity is a good thing for most plants. A successful life usually means having sex with as many partners as possible. Charles Darwin put it more soberly when he said (in reference to orchids, about which he was obsessing a the time) nature abhors perpetual self-fertilisation.

Fertilising yourself is better than no fertilisation, but to be an evolutionary success as a plant it's best to avoid it when you can. While most flowers have both boy and girl bits, they usually make sure they mature at different times. There are backup mechanisms if that doesn't work but a safer way is have separate boy and girl flowers. This is more like the way we humans do it, although the same plant can have male and female blooms on the same individual.


Sometimes, as with Ternstroemia gymnanthera, things are a little blurred (to milk the punny music connection). The False or Japanese Cleyera (Cleyera being a genus in the same obscure family Pentaphylaceae - but more of that later) has plants with either male flowers (above), or flowers that look bisexual (below). All flowers have five white petals and plenty of boy bits - the stamens.


When you look closely at these two pictures you see obvious differences. The male flowers, as is often the case for 'unisexual' flowers, have rudimentary but inoperative girl bits (you can't see these in the picture). They produce lots of pollen but no fruit and seed.

The flowers that look bisexual seem to have it all but compared to the male flowers the stamens are much smaller and shrunken back below the swollen green ovary. It turns out the girl bits work in this flower but the boy bits don't, or only hardly so.

Taiwanese study demonstrated this nicely, showing that the pollen were differently shaped in the two kinds of flowers and when cultured in sugar solution only the pollen from male flowers produced pollen tubes (needed for fertilisation). Some of the misshapen pollen in the apparently bisexual flowers became activated a little during the study but none formed proper pollen tubes.


The net outcome is plants with functionally male flowers and plants with functionally female flowers. We have both in the Melbourne Gardens, as you can see from my pictures taken in mid-January this year. The red berries, if and when they form, will only be on the latter of course. Given the sweet perfume of the flowers and their popularity with honey bees (as illustrated above) I expect a nice crop in late summer.


If you are wondering where this Ternstroemia thing fits into the plant kingdom, then you are among friends. The flowers look a lot like a Camellia, particularly something like the tea plant, Camellia sinensis. The leaves are a little like Franklinia, even reddening up occasionally as they do in that genus. With both those genera being in the family Theaceae, Ternstroemia was for a long time considered part of that family (in fact our signs in the Royal Botanic Gardens Victoria still reflect that legacy).

Nowadays, with the latest molecular evidence to hand, the False Cleyera is classified with the real Cleyera in the family Pentaphylaceae. I don't know much more about the family but it's mostly tropical. Ternstroemia itself has about 85 species, with one (Ternostroemia cherryi) extending into Queensland and Northern Territory from New Guinea. The only species in cultivation, and not widely so, is our Ternstroemia gymnanthera (the species name meaning naked anthers, a reference to the lack of bristles on the boy bits) from India through to Japan.

So, girls and boys, things are not always as they seem.

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