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Even with male and female parts in the same flower, one sex may be expressed before the other. For example, each of the many flowers in the spike-like inflorescence of skunk cabbage is female first, receptive to arriving pollen that fertilizes the egg to produce a seed, and male afterward, producing pollen that a visiting beetle may carry to another plant with female flowers.

Some plants have separate sexes, with male and female parts on different individuals; cottonwood and willow are local examples. In such species sex is determined genetically. Other plants can be female (seed-producing) in one year but male (pollen-producing) in another year. Certain exotic orchids, for example, are known to be female when large and grown in good light, but male when small and shaded. In such plants, it is apparently so expensive to be female that a plant can only do it when resources are in good supply.

A local example of a sex-changing plant is fern-leaf goldthread. If a goldthread plant produces seeds in one year, it often seems to have too little energy or too few nutrients left to make seeds again the next year. Instead, it produces a male flower that may pass on its genes by fertilizing seeds on another plant, or it may produce no flower at all, and just not reproduce that year.

A particularly fascinating case is found among ferns. The fern plant one sees in the forest is not where all the interesting things are happening. The visible fern is the nonsexual part of the life cycle: the fronds produce nonsexual spores that float away on a breeze and, when they land, germinate into a tiny, underground sexual plant that we virtually never see. The visible fern is called a sporophyte (producing spores), and the unseen little sexual plant is called a gametophyte (producing gametes - the sperm and eggs). The sperm swim over to an egg and fertilize it, and a new sporophyte grows on the gametophyte that produced the egg. In some kinds of ferns, including our bracken fern and deer fern, these tiny gametophytes can be both male and female, producing both sperm and eggs. But if one of these gametophytes gets a head start in growth, it becomes female and secretes a hormone that turns its smaller neighbors into males (at least temporarily).

The advantages of controlling the sex of the neighbors are not known, but they might include guaranteeing a good supply of sperm to fertilize the egg of the dominant female, reducing growth and resource consumption of neighboring, competitive gametophytes, or even increasing the likelihood that the suppressed neighbors will die before they get a chance to be female, thus reducing the density of future sporophytes around the one produced by the original female.

And I used to think that plants were pretty boring, biologically! Oh yes, they are essential for the oxygen we breathe, for habitats and food for animals, and for interesting landscapes. But they were boring nevertheless, because they didn't seem to DO anything. Well! When I really opened my eyes and mind, I found that they can do quite a lot, and they can be as fascinating as animals.

• Mary Willson is a retired professor of ecology and a Trail Mix board member.