Four-winged saltbush (Atriplex canescens) is normally dioecious, male and female flowers are found on separate plants. However, about 10% of four-winged saltbush plants are monoecious – both male and female flowers are found on the same plant. To further complicate the situation, a few four-winged saltbush flowers are hermaphroditic with both male and female reproductive organs in the same flower.

These three reproductive arrangements alone make four-winged saltbush an interesting shrub. Yet this plant is also capable of switching from dioecious to monoecious and back again. Fascinating!! Most often the pistillate female plant switches to a staminate male plant (protandry), but the opposite change from male to female (protogyny) also occurs. The sex of four-winged saltbush is not fixed genetically. Researchers have determined that about 40% of the shrubs in a population change sexes over a period of 7 years. About 20% do so every year.

The male staminate four-winged saltbush flowers are tiny, yellow and occur in globular clusters. These male flowers, which have anthers and shed pollen, usually occur in harsher micro-environments. The pistillate female flowers occur in elongated clusters 2 to 16 inches in length. Female flowers only produce seeds.

Environmental factors, such as an unusually cold winter, drought or an atypically heavy fruiting season, are believed to initiate or influence sex-switching in four-winged saltbush.

Male shrubs that turn into female plants are able to flower earlier in a good year and confer a reproductive advantage over regular female plants. The net result of all this sex-switching (back and forth) is that sex ratios become skewed and segregated along gradients of environmental quality. Female plants predominate in richer sites where they can become larger and produce fruits of higher quality. The male plants are marginalized to less desirable locations.

Other common names for four-winged saltbush are wingscale, chamiza, salt sage, four-wing scadshale, among others.

More information about four-winged saltbush can be found in my earlier post (“Four-winged Saltbush” 10-22-12).

What an interesting shrub!!

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2 Responses to Sex-switching

  1. What a fascinating read and an informative post. Amazing how nature overcomes harsh situations with different solutions. Am getting my tongue around ‘protandry’ and ‘protogyny’ (as is predictive text) – as in polygamy/polyandry. Great terms for general knowledge quizz 🙂

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