Plants life form

The Raunkiær system is a system for categorising plants using life-form categories, devised by Christen C. Raunkiær. It was first proposed in a talk to the Danish Botanical Society in 1904 and briefly described in the society's journal Botanisk Tidsskrift. A fuller account appeared in French the following year. Raunkiær elaborated further on the system and published this in Danish in 1907. The original note and the 1907 paper were much later translated to English and published with Raunkiær's collected works.

Raunkiær's life-form scheme has subsequently been revised and modified by various authors, but the main structure has survived.

Raunkiær's life forms: 1. Phanerophyte; 2-3. Chamaephytes; 4. Hemicryptophyte; 5-9. Cryptophytes; 
5-6. Geophytes; 7. Helophyte; 8-9. Hydrophytes. Therophyte, aerophyte and epiphyte not shown

The subdivisions of the Raunkiær system are based on the location of the plant's growth-point (bud) during seasons with adverse conditions (cold seasons, dry seasons):

Phanerophytes

Projecting into the air on stems – normally woody perennials - with resting buds more than 25 cms above soil level, e.g. trees and shrubs, but also epiphytes, which Raunkiær separated out as a special group in later versions of the system. May be further subdivided according to plant height in megaphanerophytes, mesophanerophytes and nanophanerophytes and other characters, such as duration of leaves (evergreen or deciduous), presence of covering bracts on buds, succulence and epiphytism.

Chamaephytes

Buds on persistent shoots near the ground – woody plants with perennating buds borne close to the ground, no more than 25 cms above soil surface, e.g. bilberry and periwinkle.

It is distinguished from a shrub by its ground-hugging stems and lower height, with overwintering perennial woody growth typically less than 10–20 cm tall, or by being only weakly woody and/or persisting only for a few years. Small, low shrubs such as lavender, periwinkle, and thyme, and many members of the family Ericaceae, such as cranberries, are often classed as subshrubs.

A Chamaephyte or dwarf-shrub is a plant that bears hibernating buds on persistent shoots near the ground – usually woody plants with perennating buds borne close to the ground, no more than 25 centimetres (9.8 in) above soil surface. Chamaephytes are especially important in stressful environments, for example in alpine, arctic or dry ecosystems, often grazed by herbivores, and on nutrient-poor soils or rock. Prominent examples are many of the species of maquis and other submediterranean dry ecosystems (such as thyme, Thymus vulgaris, and rosemary, Rosmarinus officinalis), the different heather species (e.g. Calluna vulgaris and Erica species), African wild olive (Olea europaea ssp. cuspidata) and edelweiss (Leontopodium alpinum). The term chamaephyte is particularly used within the context of Raunkiær plant life-forms. Chamaephytes also include cushion plants.

Prostrate shrub is another similar term.

One significance of the closeness to the ground is that the buds remain within the surface boundary layer and are thus somewhat protected from harsh winter winds.

Hemicryptophytes

Buds at or near the soil surface , e.g. daisy, dandelion.

Protohemicryptophytes: only stem leaves

Partial rosette plants: both stem and basal rosette leaves

Rosette plants: only basal rosette leaves

Cryptophytes

Below ground or under water - with resting buds lying either beneath the surface of the ground as a rhizome, bulb, corm, etc., or a resting bud submerged under water. Cryptophytes are divided into 3 groups:

Geophytes: Resting in dry ground, e.g. crocus, tulip. May be further subdivided into rhizome, stem-tuber, root-tuber, bulb and root geophytes.

Helophytes: Resting in marshy ground, e.g. reedmace, marsh-marigold. A helophyte or limnodophyte is the phytosociologic definition of a biennial or herbaceous plant of which only the buds survive a harsh period, such as winter, e.g. sweet flag (Acorus calamus) or bulrush (Typha sp.). Many helophytes can also be termed hydrophytes or aquatic plants, e.g. common duckweed (Lemna minor), eelgrass (Zostera sp.), and water soldiers (Stratiotes sp.), or geophytes, e.g. the yellow flag (Iris pseudacorus).

Hydrophytes: Resting by being submerged under water, e.g. water-lily, frogbit. Aquatic plants - also called hydrophytic plants or hydrophytes - are plants that have adapted to living in or on aquatic environments. Because living on or under water surface requires numerous special adaptations, aquatic plants can only grow in water or permanently saturated soil. Aquatic vascular plants can be ferns or angiosperms (from a variety of families, including among the monocots and dicots). Seaweeds are not vascular plants but multicellular marine algae, and therefore not typically included in the category of aquatic plants. As opposed to plants types such as mesophytes and xerophytes, hydrophytes do not have a problem in retaining water due to the abundance of water in its environment. This means the plant has less need to regulate transpiration (indeed, the regulation of transpiration would require more energy than the possible benefits incurred)

Therophytes

Annual plants which survive the unfavourable season in the form of seeds and complete their life-cycle during favourable seasons. Annual species are therophytes. Many desert plants are by necessity therophytes.

Aerophytes

New addition to the Raunkiaer lifeform classification. Plant that obtains moisture (though not through haustoria) and nutrients from the air and rain; usually grows on other plants but not parasitic on them.

Epiphytes

see Phanerophytes above.

It is  a plant that grows upon another plant (such as a tree) non-parasitically or sometimes upon some other object (such as a building or a telegraph wire), derives its moisture and nutrients from the air and rain and sometimes from debris accumulating around it, and is found in the temperate zone (as many mosses, liverworts, lichens and algae) and in the tropics (as many ferns, cacti, orchids, and bromeliads) - called also air plants."

Epiphyte is one of the subdivisions of the Raunkiær system. The term most commonly refers to higher plants, but epiphytic bacteria, fungi (epiphytic fungi), algae, lichens, mosses, and ferns exist as well. The term epiphytic derives from the Greek epi- (meaning 'upon') and phyton (meaning 'plant'). Epiphytic plants are sometimes called "air plants" because they do not root in soil. However, there are many aquatic species of algae, including seaweeds, that are epiphytes on other aquatic plants (seaweeds or aquatic angiosperms).

Epiphytic organisms usually derive only physical support and not nutrition from their host, though they may sometimes damage the host. Parasitic and semiparasitic plants growing on other plants (mistletoe is well known) are not "true" epiphytes (a designation usually given to fully autotrophic epiphytes), but are still epiphytic in habit.

Epiphytic plants use photosynthesis for energy and (where non-aquatic) obtain moisture from the air or from dampness (rain and cloud moisture) on the surface of their hosts. Roots may develop primarily for attachment, and specialized structures (for example, cups and scales) may be used to collect or hold moisture.

Epiphytic plants attached to their hosts high in the canopy have an advantage over herbs restricted to the ground where there is less light and herbivores may be more active.

Reference: Raunkiær, C. (1934) The Life Forms of Plants and Statistical Plant Geography. Introduction by A.G. Tansley. Oxford University Press, Oxford.