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Asexual Flora

Plant Reproduction Done Solo


Monday, July 30, 2012

Sex is the usual way to reproduction of a species. In the animal world, a hen’s egg is fertilized by rooster sperm, papa frog spills his swimmers over the mama’s eggs (sometimes after manipulating her to lay them), and, well, humans have their own twist on courtship and procreation. Some of those offspring are nurtured outside the parental bodies — left in (hopefully) secure external environments to hatch and forge their own destiny. In humans, of course, that embryo not only grows inside the mother, but needs many years of care once it is born to reach maturity.

Plants do things quite differently. Male pollen grains are wafted on the wind, fall gently by gravity, or ride piggy-back on any number of creatures from beetles to bees and even small rodent noses to make contact with the stigmas of their female counterparts. Fertilization takes place without any conscious help and minimal post-coital care. In spite of this, plants have thrived and sent waves of successful progeny out into the world to multiply or at least hold their own in their particular habitat.

Some plants, however, have another reproductive “strategy” that sidesteps the whole messy sex thing. They can produce a separate, new, individual from just a twig, leaf, or root segment. These newly minted plants are clones of the parent, having the exact genetic makeup. Sometimes this can be a good strategy; other times it can lead to loss of adaptability. The genetic mixing that happens in sexual reproduction generally leads to preserving the diversity of a species, while asexual reproduction only preserves a single set of genetic traits.

Examples of this kind of celibate progeny are found in plants such as the invasive grasses like crabgrass and kikuyu grass. Their horizontal stems spread out and root wherever a node touches the ground. Grasses do it on the surface, while other plants, like mint, do it underground; sending out runners that produce a sprout above ground. Other plants, like begonias, can produce plantlets from their leaves, again, if they encounter the optimal conditions.

Some plants are more proactively procreative. Almost everyone knows the houseplant Chlorophytum comosum. In some places, it is called airplane plant and in others, spider plant. Both common names refer to its habit of sending out aerial shoots that produce whole miniature plants at their ends. These plantlets root easily, whether still connected to mama or not.

Another common name that tells the same story is mother fern, assigned to Asplenium bulbiferum. All along the fronds of this ornamental fern, unrooted but viable baby plants sprout. Should they make contact with a suitable surface for rooting, usually the soil below their mother, they will readily root and grow. Another fern, the chain fern (Woodwardia fimbriata) can also produce another separate plant, usually only where the arching frond actually comes into contact with the soil.

It’s not just ferns and begonias; plants that thrive in moist environments have evolved structures that optimize their reproductive success. Some succulent plants, normally growing in quite arid environments, also produce viable asexual progeny. Maternity plant, Kalanchoe daigremontiana, is also aptly named. Each daintily scalloped succulent leaf is capable of producing dozens of tiny new plants. Even before they fall from the parental unit, these little plants are sending out fine threads that can root immediately on contact with the soil. Gardeners have long passed these plants around because of the ease with which they can be propagated.

August Tips

• Mid to late August is the perfect time to start seeds of cool-season crops like cabbage, broccoli, and spinach. Plants will be ready to move into the garden in six to eight weeks.

• Divide bearded iris: Dig and cut off new stems, discarding woody center of clump. Replant immediately or store in damp peat moss in a cool place for planting early next year.

• Harvest potatoes, onions, and garlic only after their foliage has fallen over and dried out.

Related Links

Virginia Hayes, curator of Ganna Walska Lotusland, will answer your gardening questions. Address them to Gardens, The Independent, 122 W. Figueroa St., S.B., CA 93101. Send email to vahayes@lotusland.org.

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