Plant reproduction: sexual and asexual propagation


Sex acts are taking place in your garden. The birds, bees and the flowers in the trees are all involved. Flowers are the sexual organs of plants. Their blooming periods, as well as their attractive colors, alluring shapes and provocative fragrances all serve to attract pollinators. Getting the right bird or bug in the right place at the right time is paramount to the continuation of the plant species.

The pollinator’s role in the plant’s life cycle is to move pollen from the anthers, or male parts of the flower, and transfer it to the stigma, or female parts of that flower or another flower of the same species. The pollen lands on the sticky surface of the stigma the travels down the style to the ovary. Once the female ovary is fertilized by the male pollen, seeds begin to form often surrounded by fruit. These seeds represent the next generation in the life cycle of that species.

Though this process can have lots of variation and complexity depending on the plant, sexual reproduction is taking place daily in Hawaii, where flowers bloom year-round. With a few exceptions, fruiting plants have seeds within the fruit. At this point in the plant’s life cycle, another design feature is at work. The fruit, containing the seeds is designed to be attractive to living, mobile species that can spread the seeds. Fruit can be colorful, sweet, barbed or simply imitative of something delicious. Someone or something is going to eat it or brush against it and carry the seeds to a new place. Distribution is thus accomplished.

In an ideal place, the seeds will germinate and grow into new plants and the cycle repeats. All this was taking place in the plant world millennia before humans got the brilliant idea of purposefully collecting and saving the seeds of plants they liked in order to plant them in the future.

Seed saving was the basis of modern agriculture and though it is threatened today by recent legislation and corporate patent laws, we can still save seeds from most of our plants. The simple act of saving seeds from this season’s harvest and planting it the next or sharing it with a friend is an important act. Each new generation of seeds selected from the best parent plants will likely produce plants that are better adapted to their environment and will be slightly improved.

Ancient farmers learned other ways to reproduce some of their favorite plants asexually, without the use of seeds. Many plants produce keiki from underground expansion of corms, bulbs or root shoots. Others may produce above ground runners or ground level branches that will root.

Once humans got involved, the asexual options expanded to propagation by cuttings, layering, grafting and tissue culture. Though the best propagation technique varies by species, many plants can be propagated in several of these ways. Some of the plants that self-propagate easily have become weedy pests that are hard to control. Many attractive garden plants and delicious edibles, however, can be reproduced successfully asexually.

New plants grown from seed contain the genes of both the male and female parents and may not exactly duplicate either parent. Plants that are propagated asexually are clones of their single parent and will be exact duplicates. Deciding how to add new plants to your garden is determined by the choices the plant offers, as well as personal preference.

Next Saturday, gardeners, farmers and plant lovers will be gathering at the Summer Seed Exchange to share seeds, cuttings, corms, bulbs, runners and root shoots with one another starting at 1:30 p.m. at Tropical Edibles Nursery in Captain Cook. At noon, an opportunity to share food and stories about seed saving will be part of the potluck lunch. The event is free and open to the public.

Participants in the exchange are encouraged to bring information about their plant material, including the best growing techniques. To avoid possible spreading of little fire ants, folks are requested not to bring plant material in soil. Bring envelopes and pens to record information on what you take home. You are welcome to participate even without plant material to offer this time. Acquiring new plants and information now will mean you’ll have material for the next exchange. If you can’t make this exchange, start saving seeds for the next event. Exchanges usually occur twice a year in West Hawaii.

Tropical gardening helpline

Carol asks: When identifying trees on my new property, a friend told me that one of the trees with orange flowers was a jacaranda. I have not been able to find any jacarandas with orange flowers listed anywhere. Do you know of one?

Answer: Jacaranda (Jacaranda mimosifolia) trees have light blue or purple flowers. Your friend may be thinking of the African tulip (Spathodea campanulata), which does have orange flowers and is in the same family (Bigoniaceae) as the jacaranda. The African tulip is also a large tree like the jacaranda and also has tubular flowers. The tiny leaflets of the jacaranda are doubly pinnate, giving them a fine textured appearance. African tulip leaves are similarly arranged but are single pinnate leaves with larger leaflets and a coarser appearance.

The royal poinciana (Delonix regia) tree might also be confused with a jacaranda because the fine textured leaves are very similar. The flowers are orange but have a very different shape from jacaranda. They are fully open with five bright orange or scarlet petals and occasionally have one spotted white petal. Royal poinciana is in the Fabaceae family.

It is very easy to get confused in tree identification when the plant is not flowering. As always, the distinguishing feature that defines the plant’s identification is the flower.

Email plant questions to konamg@ctahr.hawaii.edu for answers by certified master gardeners. Some questions will be chosen for inclusion in this column.

Diana Duff is a plant adviser, educator and consultant living on an organic farm in Captain Cook.