Bauhinia and Hibiscus: A Comparison of Floral Reproduction

This posting is a response to the numerous hits made on a previous posting featuring the Non invasive Bauhinia tree. It seems that the interest lies in its reproductive nature. The purpose of this post is to improve the understanding of plant biology through comparative anatomy.

The title image shows the Bauhinia (blakeana ) on the left and the Florida native scarlet rosemallow (Hibiscus coccineus) on the right. I photographed the Bauhinia in the roadway median of our neighborhood. I photographed and display the scarlet rosemallow because it is such a stunning finding in the fresh water marshes of the Corkscrew Nature Preserve in SW Florida. It also shows that it is not a cultivar but it can self propagate without human intervention. Both plants are eye candy that must be appreciated in their out-of-door surroundings. In our community we have domesticated tropical hibiscus which are close relatives to the wild scarlet hibiscus

These two blossoming plants attract loads of attention. The Hong Kong orchid (Bauhinia blakeana ) and the cultivated tropical Hibiscus (Malvaceae) produce wonderful, flamboyant, visually attractive flowers. They are planted throughout our community. Additionally, these blooms have great staying power lasting for many months. Their flowering period stretches anywhere from eight to ten months, from September to June. They have, however, remarkably different reproductive powers. To reveal the secret of these two plants this posting compares the gross and micro anatomy of their two flowers.

Gross and micro dissection reveals the major difference in the reproductive capacity of the these two perfect flowers. Dissection and microscopic examination of the ovaries shows that the hibiscus has ovaries while the bauhinia has no trace of ovules. It is unable to sexually reproduce.

The five-petaled blossoms of Bauhinia plants are known as “perfect flowers,” because each individual bloom contains both female and male parts. Some varieties of the Bauhinia flower, such as the widely cultivated Hong Kong Orchid Tree (Bauhinia × blakeana), are known to be sterile. Bauhinia are monoecious, which means “single house”. This designation describes the dual sexual capacity in a single flower. The flowers can self pollinate or fertilize with pollen from another plant. The flowers attract pollinators such as hummingbirds, bees, butterflies, and more. Bauhinia × blakeana‘s sterility is due to its hybridization. Bauhinia blakeana is the result of conjugation of the very similar species Bauhinia purpurea ( Purple Camel’s Foot) and Bauhinia variegata ( Camel’s Foot Tree). Both of these are exotic species according to the Hong Kong Herbarium. The parent plants have partially overlapping flowering periods and geographical habitats, and the same range of bee and butterfly species as pollinators. Interbreeding Bauhinia purpurea and Bauhinia variegata is probable. The resulting triploidy of this plant has probably rendered this varietal sterile. The plants you see today are clones of the same flowers seen by Hongkongers more than a century ago. They are propagated asexually through cultivation of stem cuttings.

The Hibiscus is also considered a perfect flower which actually produces viable seeds. The hibiscus is a genus of flowering plants known for their large, showy flowers, belonging to the mallow family (Malvaceae). Fertilization of these plants is complex. Pollination may fail because of these five prerogatives.

• Self-Pollination: Some hibiscus varieties are self-pollinating. This can make it difficult to cross-pollinate them.
• Timing: Hibiscus flowers are only receptive to pollen for a short period, usually just a few hours.
• Pollen Viability: Hibiscus pollen can lose its viability quickly.
• Stigma Receptivity: The stigma needs to be receptive to pollen. The stigma, gateway to the ovarian, might not be receptive at the same time the pollen is viable.
• Germination: Seeds take 12 to 24 months to bloom.

The hundreds of species of hibiscus are generated through human intervention of the pollination. Tropical hibiscus are propagated sexually from seeds or asexually from stem cuttings or plant division. In carefully controlled environments and with delicate, patient effort botinists have hybridized the tropical hibiscus to make hundreds of beautiful new varieties. The new plant varieties are propagated from cuttings or division to produced plants which are clones of their parents.

DISCUSSION of FINDINGS:

This is not a thorough scientific data collection. Three samples of blossoms from each of two trees were collected for a total sample size of six. All of the samples were made on the same day in April, 2020. There were no major local meteorological events for the year preceding this observation. There were no observations of the viability of the observed polled during this observation. Further study should be done to give this a high level of confidence of the conclusions.

SUMMARY:

In Florida the Bauhinia × blakeana and Hibiscus plants thrive and are found in almost all of the cultivated communities and household gardens. They are well tolerated but stable non-native species. Because of their reproductive limitations they are not invasive. We can feast our eyes on this banquet of form and color without fear of damaging the environment.

REFERENCE LINKS:

• The Bauhinia blakeana needs human hands to be propagated.
• Orchid Trees.
• Hibiscus classification.
• Hibiscus propagation.
• Hong Kong Herbarium

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