dehisce [ dih-HIS ] verb: to split or burst open (noun: dehiscence)
In botany, the word dehisce is used mainly when discussing plant parts such as anthers, sporangia, and fruit. The dehiscence of an anther is timed to synchronize with the maturation of the flower and its opening. Within an anther lobe (theca), thin-walled cells of the stomium separate the two sac-like structures (microsporangia) in which pollen grains develop. When the surrounding tissue dries, the stomium splits open or dehisces and the anther’s pollen grains become accessible to pollinators. The split can occur along the anther lobe’s length (longitudinal dehiscence) or width (transverse dehiscence), or through pores at its tip (poricidal dehiscence) or under its tissue flaps (valvular dehiscence)
Not all fruits are dehiscent. Fleshy fruits like berries, drupes, and pomes, and dry fruits like achenes, cypselas, and nuts are indehiscent. The dry fruits that do dehisce are follicles and most legumes and capsules. They split open along one or more seams or sutures, exposing their seeds. Follicles, like those of columbine and milkweed, split lengthwise along one suture. Like the fruits of blue wild indigo and redbud, legumes split lengthwise along two sutures. Capsules, on the other hand, dehisce in various ways. Some split longitudinally from top to bottom into distinct segments called valves, such as the 3-valved daylily and violet or the 5-valved hibiscus. Other capsules, like those of plantago and twinleaf, split transversely so that an upper, lid-like portion opens. The poppy splits poricidally with the opening of round holes. In these examples, the seeds usually remain in the dehisced fruit until they are dispersed by wind (milkweed and poppy), water (hibiscus), or animals (violet) or succumb to gravity, topple over, and spill out on the ground (columbine and wild indigo). Besides depending on ants to transport their seeds, violets also can scatter their seeds explosively after dehiscence. As the capsule valves dry, they fold inward exerting pressure, which expels the seeds.
Left to right: Hemerocallis (immature and dehisced capsules), Hibiscus coccineus (immature, dehiscing, and fully dehisced capsules), Jeffersonia diphylla, Plantago major, Papaver orientale.
However, sometimes dehiscence itself can be explosive. Some fruits ballistically eject their seeds as they dehisce. Just one drop of water can explode a ripe Impatiens capensis (orange jewelweed) capsule. The elongated valves dehisce tightly coiling inwards, ejecting the seeds up to six feet away, hence another of its common names: touch-me-not. (Watch Smithsonian channel Seed Dispersal by Explosion video.) Likewise, slight contact with a dry Oxalis stricta (common yellow wood-sorrel) capsule will split it open, shooting out individual seeds in rapid succession up to 10 feet away. (Watch Wood-sorrel Seedpod Explosion video.) As the long slender siliques of Cardamine hirsuta (hairy bittercress) ripen, their tissues swell, increasing internal pressure to a point at which they explode, dispersing seeds (hundreds per plant) potentially up to a distance of 16 feet. The curled valves of the siliques remain connected at the top. When the seeds of Geranium maculatum (wild geranium) are ripe, the capsule splits, curling upward and backward, ejecting the seeds up to 30 feet from the parent plant.
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