Other than its position in the phylogenetic tree, each plant is also defined by it’s “place of birth”. As time is the magician, while location is the three-dimensional space that carries its own secret codes such as humidity, light intensity, temperatures, and soil composition et al. From algae-like plants to higher flowering plants, from aquatic environments to terrestrial environments, from knowns to unknowns. Plants grow in most areas of the earth including some really harsh conditions. The location could be a lake, a wetland, high mountains, deserts, acid or salty land. According to their growing conditions, there are at least five major ecological classifications that every plant lover needs to know. The benefits of knowing these different groups are helpful with choosing the correct growing methods and for better horticulture practices. At least to avoid mix aquatic plants with desert plants in the same pot. Mainly the groups are hydrophytes, hygrophytes, mesophytes, xerophytes, and halophytes. (-phyte, -phyta, and -phytic means plant or plant-like in Greek).
Hydro in Greek means water. Hydrophytes are plants that adapt to aquatic conditions. The characteristics including finely divided submerged leaves, large floating leaves, or sometimes altogether absent, the presence of aerenchyma, and the reduction in the root system. Aerenchymatic tissue has large and intercellular air spaces which contribute buoyancy force for the species to be free-floating in/on the water. For some species, the perennating buds lie at the bottom of reasonably open water with the leaves submerged or floating. The only organ that protrudes above the water surface is the inflorescence, the beautifully arranged flower with high ornamental values. Underwater leaves of hydrophytes have no stomata, except the leaves floating on the water surface and stomata are found on their upper surface. Their stems are usually soft and weak since the vascular system is poorly developed as they can get the nutrients and water directly in the water. Moreover, soft and flexible stems allow them to withstand the strong water current or flow so that they will not break into parts in the strong water current. These hydrophytes can be further categorized into submerged, free-floating, and amphibious. A typical example of this group is water lily.
Subsequently, hygrophytes, hygros in Greek means wet. The plants of this group are living above ground, shade-loving plants that always found at a high moisture environment. The main characteristics of hygrophytes are that they have soft and spongy stems and roots which always show stunted growth. Their stem is mostly modified and specialized into underground rhizome which is an organ that is crucial for propagation. Hygrophytes have well-developed and rounded leaves that possess stomata. However, their transpirational rate is relatively low as they grow in a shady and moist environment such as a forest. Therefore, the excess water is expelled through a special opening called water stomata, or botanically known as hydathodes. The plants in this group are at least resistant to drought. The typical example would be some kinds of ferns. Fern can also be mesophyte and xerophyte as well as epiphyte though.
The following group is mesophytes, in which the plants thrive the best on a moderate supply of water. Mesophytes also referred to those plants that adapted to the environment neither extremely wet nor extremely dry. They usually have well-developed roots and leaves that help them to live in a favorable condition for optimal growth. In addition, mesophytes include large and fast-growing plant species with big leaves that protected with a cuticle layer and thin epidermis. Their stem can be either herbaceous or woody with developed vascular tissues, and differentiated tissues that provided mechanical strength to support the plants. Generally, mesophytes are considered as normal plants and do not have any special morphological traits. Therefore, they tend to lose water more rapidly and intolerant to drought conditions when they exposed to extreme conditions. For instance, they may suffer temperature stress in hot weather. However, they are some exceptional mesophytes such as a deciduous tree, which is mesophytic during the summer and xerophytic in the winter. Most garden plants and crops are in the group such as garden roses.
The next group is xerophytes, sometimes referred to as zerophytes. Commonly known as drought-loving plants, this is a group of plants that can grow in arid conditions and can withstand periods of drought. The adaptation traits include the fleshy tissues that can store water, waxy leaves with thick cuticle layers, modified leaves that reduced to spines to avoid water loss et al. They usually have short life cycles, botanically known as ephemeral, that can be complete when sufficient water is available. There are further categories for this group which are the xerophytes that grow in uniform dryness and periodic dryness. The plants grow in regular drought may be referred to as drought-tolerant plants. Rock plants also fall into this category which is resistance against the frequency of periodic dryness and extreme desiccation. The typical examples of xerophytes are cactus and succulents.
The last introduced group is halophytes. Halophytes are the terrestrial plants that adapted morphologically and/ or physiologically to grow in salt-rich soils and salt-laden air. They are known as salt-tolerant species. The plants inhabit saline soil with high concentrations of salts such as sodium chloride, magnesium chloride, magnesium sulfate, which is physiologically a dry soil, or saline water. Interestingly, halophytes have succulent leaves and stems. They have fleshy leaves that have water storage tissues but their stomata always sunken. Such xerophytic-like characteristics are the results of the adaptation towards the rection of excessive salt on the plants. Halophytes can be the trees found at mangrove swamp, typically Rhizophora and Avicennia.
Other types of -phytes that are not discussed above but should be mentioned here as well. For instance, psammophytes are the plants that grow on the sand. The plants that grow in the crevices of rocks are classified as chasmophytes. Oxylophytes are the type of plants that adapted to grow at acidic soil. Lithophytes refer to the plants that grow on the surface of rocks. Psychrophytes are the plants that grow on cold soils. Plants grow well on wasteland are grouped as chersophytes. Eremophytes grow on deserts and steppers. Xerophilous plants growing at savannah are grouped as psilophytes. Those species that are adapted to forest and bushland are known as sclerophytes. Epiphyte, which grows in the air and does not have a permanent connection with the soil, is one of the symbiotic relationships with their host plants.
Wow! Literally, plants can live anywhere, and everywhere. Actually astronauts have already start to grow plants in the outer space, and maybe will build a farm on moon or mars. Plants are so ready for unknowns. Do you have a name for those plants? Put you comments by the end of this article.
Further reading:
Schulze, E-. D., Beck, E., Műller-Hohenstein, K., Lawlor, D., Lawlor, K., & Lawlor, G. Plant Ecology. 2005. Springer.
Zhang, X., Wang, M., Liang. X. & Van der Valk, A. G. Forest ecology: recent advances in plant ecology. 2009. Springer Netherlands
