One-petalled flower not really

Begonia guru Peter Sharp says the so-called 'Rex Begonias' are usually grown indoors although he has seen them grown successfully in gardens (Peter wrote the book from Sydney and is now in Tasmania, offering up two quite different prospects for these plants I'd suggest). We have one of them, growing sort of outdoors in Melbourne, in a pot.

It's a few weeks since our plant flowered but talk of the Begonia Festival at Ballarat Botanical Gardens over the weekend, reminded me of its odd flowers. As mentioned last time I was diverted by a Begonia, the genus is usually split into eight informal groups.

One of these groups contains begonias with an underground stem (rhizome) rather than a tuber, and with a recent ancestor (prior to breeding) called Begonia rex from India. The cultivar we are growing (photographed here) may have a little of another species, Begonia mesoniana (the Iron Cross Begonia), in its family history but this post is not about taxonomy (that is, I haven't confirmed its identity...). With its distinctive habit and coarse hairy leaves I'm presuming it nestles somewhere near Begonia rex. and is therefore a member of the rather sinisterly named Rex Cultorum Group.

With a light sprinkle of water each morning our Rex devotee grows quite nicely on our front porch, flowering happily in January and February.

Most growers don't grow begonias for their flowers. In fact the usual advice is something like 'cut the flowers and allow the plants energy to go into growing the leaves'. If you ignore this advice you'll be at least mildly intrigued by what looks like a single petal in some flowers. Which is very odd.

Begonias have separate male and female flowers, both on the same plant and mostly both within each terminal cluster. In our plant there were only female flowers open when I took the first photographs (11 January; above and top of post), and the male flowers (without the large deep red ridged structure so apparent in this picture) only in bud. Two weeks later (below) it was all about the male flowers, although with a few females still waiting to open later (see the bud heading downwards to bottom left).

The flowers are described as having four or five 'sepals' and no petals. Not one or two, none. But...although the sepals in most plants are usually the outer ring of greenish bits, in begonias they usually more colourful and look pretty much like petals. This is why they are often described as petaloid sepals.

In those blousy blooms you see on tuberous begonias at places like Ballarat Botanical Gardens, I'm presuming the anthers are all converted into petal-like bits as they are in Hellebores. This gives the impression of a profusion of petals.

In nature and in many other species there are just four or five of those colourful floral bits. Sometimes they look the same as each other but you can also get two plate-like petaloid sepals, and two narrower and smaller segments. Oddly, in this particular case the female flowers have two big ones and just one of the second tier. So that's three in total unless one is very tiny (which it may be). That's almost as odd as having one petal!

The male flowers are more conventional, having two outer parts and two of the petaloid sepals inside. The yellow pom pom is of course a cluster of stamens tipped with yellow anthers (full of pollen).

Searching the web I see there are other examples (but not many) of the female flower morphology. One example is the Chinese species Begonia fimbristipula, whose leaves are used for making a tea-like drink. So it's not just a odd reaction by the plant to the Melbourne porch climate.

The pot, moved out of the porch, for its portrait.