Xerophytes
Xerophytes live in environments with little or no water in abundance most of the times. Therefore the stem and xylem of xerophytes have developed to transport water and provide structural support for the plant as well as storing water, protecting that water, and in most cases, photosynthesising as well.
Stems of xerophytes have adapted to store water by containing large quantities of the succulent tissues that can absorb and store water and they also have ridges in their stems to allow sudden expansion for maximum storage of water when there are sudden rainfalls.(KadavansKolothum, 2015) (NinErrin, 2015 ) (DimmittMark, 2015)
They have adapted to protect this stored water by having thick waterproof cuticles on their top layer which decreases the amount of water being lost via evaporation and also having spines on their stems to provide protection against predators looking for water sources. Their water sources are also usually bound in extracellular mucilages and insulins (soluble fibers) that only releases water reluctantly so that even if a part of the plant is broken off, the insides stays moist for a long period of time as without this feature, once the plant’s precious water supply is exposed to the harsh environment of xerophytic plants with winds, heat and light, it will be gone. (onlinebotanical, cactus adaptations, 2015) (HenryEllen, 2015) The stems of xerophytes have a greenish colour as it is the main site of photosynthesis as most xerophytes do not have leaves. The stem also photosynthesises by C-4 or CAM photosynthesis by obtaining and storing carbon dioxide at night while photosynthesising at day to conserve water. The xylem of xerophytes have similar adaptations to the xylem of mesophytes as they both adapted to provide structural support to the plant and transport water around the plant. However, the xerophytic xylem has extra supporting tissues so that even when the plant wilts due to the lack of water, it won't completely collapse. (PentecostCaroline, 2015) (DimmittAMark, 2015) (DimmittMark, 2015) (onlinebotanical, cactus adaptations, 2015) If xerophytes were to have thin and flexible stems like hydrophytes with little or no protective tissues, it will wilt and lose water via transpiration and evaporation very quickly. If xerophytes were to have the stems of mesophytes, it might be able to survive the wet periods but will quickly wilt and die as it doesn’t have the extra strengthening tissues that keeps the plant from completely collapsing as it wilts and cannot store any water it obtained during the wet periods to slowly distribute around the plant in the dry periods. |