I became intrigued about the mad skills my-most-hated-weed has and decided to research them and share with you how amazing this plant is, in terms of doing its best not to ever die! The common name is Benghal dayflower or Commelina benghalensis, and it is in the Commelinaceae family. Commonly known as tropical spiderwort and other non-politically correct names, like wandering Jew. It sure does wander and it wanders fast! Any moisture will necessitate rampant lush growth that will quickly cover other plants (Figure 1).
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| Figure 1. Commelina benghalensis S. Reeve |
Commelinaceae Family
The Commelinaceae are annual/perennial herbs with succulent stems and swollen nodes. The family is named after a Dutch botanist, Caspar Commelijn, 1667-1731. Worldwide, there are approximately 170 species, with the majority originating in Africa and tropical Asia. The family is characterized by leaves that spiral around the stem, each leaf forming a closed sheath around the stem (Figure 2). The above-ground flowers are hypogynous, with the ovary above floral structures. The corolla (C), or petals are ephemeral and occur in threes, and are either blue or white in color. An evolutionary novelty of this family is the presence of 3-celled glandular microhairs, which are really tiny hairs, for lack of a better term, and invisible to the naked eye. The term glandular means they produce some kind of secretion; although, I could never find out the identity of the secretion. The hairs are thought to reduce herbivory and transpiration, and are sunlight-reflecting, thereby, decreasing moisture loss.
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| Figure 2. Leaves sheath stems completely Image from Invasive.org, Herb Pilcher USDA |
This monocot was a recent arrival to Southern California in the eighties. As the common name dayflower suggests, the above ground flowers are open during the day (Figure 3). Commelina benghalesis is closely related to Commelina communis or asiatic dayflower. It is difficult to tell them apart at first glance, but they differ in that Commelina benghalensis is hairy, the flowers are a lighter blue color, and the plant has underground flowers (more on THAT later), and longer leaves. All members of the genus Commelina have bilaterally symmetrical flowers with three fertile stamens, three staminodes, and a reduced lighter-colored anterior petal (Figure 3).
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| Figure 3. Commelina flowers S. Reeve |
Survival Skills
This is the good part when we get to talk about the terms cleistogamous and chasmogamous flowers! This is one of the most difficult plants to kill for a number of reasons. Because of its succulence and its various evolutionary strategies for reducing water loss, you can pull it and throw it nearby, and it will remain viable until it rains, at which point, it will quickly send down roots. For this plant, I must either pull it and throw it onto the concrete, or bag it and throw it away (the loss of biodegradable plant material kills me). So for these reasons alone it is difficult to kill. Secondly, it is stoloniferous and it grows and roots at the nodes (Figure 4). Studies found that the rate of stem elongation, and branch and leaf formation increases as the number of nodes increases, so it directs it resources to the larger and more successful growth areas. This is truly a well-adapted plant for survival! It flowers at the nodes too, and each flower produces seeds. Additionally, in periods of low rainfall, the plant curls its leaves and the leaves take on a grey color to wait it out until it rains. Plants can remain in this torpor state for a remarkably long time! Typically an annual, with periods of high rainfall it can become a perennial, so it is highly adapted to survive.
This plant can also reproduce either sexually or asexually, increasing its chances for survival. To reproduce sexually, it produces aboveground flowers during times of environmentally favorable conditions (Figure 3) . This reproduction scheme forms pollen-producing chasmogamous flowers (most flowers are chasmogamous). Chasmogamous means "open marriage." Chasmogamous flowers take more plant resources and energy because they are larger and more complex, with nectar guides, and other features, to attract pollinators. In the case of Commelina benghalensis, the elaborate, but pollenless, stamenodes serve to visually attract pollinators because they appear to be loaded with pollen. Bait and switch--so underhanded!
Commelina benghalensis is also considered to be andromonoecious meaning that it produces both male and bisexual flowers on the same plant. This floral strategy is thought to promote cross-pollination.
During difficult environmental conditions, it is less energetically taxing for the plant to also produce cleistogamous flowers. Cleistogamous means "closed marriage." For Commelina benghalensis, cleistogamous flowers are very small bisexual flowers, produced underground, that do not require pollination. The ratio of chasmogamous/ cleistogamous flowers is related to environmental conditions. Studies have found that the underground seeds that form are highly persistent and can remain viable until conditions are right for germination. The subterranean seeds differed from the above-ground seeds in that they required higher temperatures, and more light to germinate. All I know is when I pull it those belowground seeds break off in the soil and germinate quickly.
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| Figure 4. Rooting at nodes S. Reeve |
Clearly, if it came to a battle of survival, at the end of the world there will be cockroaches and Commelina benghalensis! Couple all of its mad survival skills with the fact it has few predators or disease, and it becomes a wonder why I bother to battle it at all! In crops it is also a serious pest because it is immune to glyphosate.
Sometimes I become a little smug and think I have a chance to win this war, and I have only to look across the fence into the neighbor's yard (Figure 5) to realize I don't have a prayer against Commelina benghalensis!
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| Figure 5. Neighbor's yard S. Reeve References on request |
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