Biennial plants are just one evolutionary strategy among many. They are all variations on a single theme, namely to gather sufficient resources to supply their reproductive needs in the form of pollen, seeds, offshoots and the like. Before they have gathered the necessary food material, energy and the like, they simply cannot reproduce.

The devil and the variety are in the details. There are whole classes of life histories. Annuals drop seeds that grow rapidly and produce more seeds perhaps a year later. Perennials such as trees may take decades or longer before they have accumulated what they need for their particular reproductive strategy, after which they continue to produce seeds, possibly year after year.

Some plants accumulate resources hugely for a long time, after which they reproduce dramatically, often in more than one mode at a time, expending all their resources at once, then dying. Agaves include many examples in one form or another. Of course, annuals could be regarded as a special case of one such strategy.

For some other plants, probably in particular some that have a history of ancestors whose annual development frequently got interrupted by cold weather and early winter before they had time to gather enough resources to produce seed in their first year, but could reproduce successfully after a second year of growth. In warm temperate or tropical climates such selection pressures would hardly occur, but in cold temperate regions it is only too believable that biennial reproduction could prove a viable strategy. But I repeat, it is just one variation on more themes than you might well believe, all based on the same principle. This kind of comparative biology is a particularly beautiful and intellectually satisfying field of study.

I hope I am not the only one to hold this opinion!

Jon

Also true in the animal world. For example, Cicada Magicicada is an insect that spends a prime number of years (13 or 17) living underground as a nymph. This is believed to be a strategy for avoidance of specific predators that evolved multi-year life cycles of their own, by being co-prime to theirs.

Then, all cicadas burrow to the surface, moult, and breed on the same day. This is believed to be an evolved strategy against general bird and wasp predators, which eat their fill but still consume only a small proportion of the mass.

Also, a story from the British Raj in India. Sometime around 1910, a group of Mizoram elders came out of the hills to ask for help. They said the bamboo had just flowered, that this happened only every 50 years, and that last time it happened many people starved to death. The British told them not to believe all the tall tales they were told, and to go away.

Sure enough, the next year millions of extra rats bred because the bamboo flowers result in edible fruit. The year after that, there was no bamboo fruit so the rats ate all the stored corn and rice that was to be planted. And the year after that, many Mizos starved to death.

And then, incredibly, the Assam (Indian) government made precisely the same mistake in 1959, triggering an insurrection that lasted nearly 30 years. And the bamboo is flowering again ... this year.