Raunkiær system

The Raunkiær system is a categorization of the forms of development or biological forms (biological types) of plants, created by Christen Raunkiær (1860-1938) (Raunkiær 1934). The subdivisions of the system are based on the adaptations of the plants to survival during the unfavorable season, mainly whether they do so as seeds or, if as adult plants, whether they lose the green parts and the location and the type and degree of protection of the plants. buds during the unfavorable season. The classification was carried out with the aim of creating geographical regions within which the conditions for plant life were more similar than in relation to localities in other regions (equiconditional regions) that were used as a basis of a Geography of plants or phytogeography. The concept was that the environmental factors present in geographical regions - mainly temperature, water, and their distribution throughout the year - find a marked expression in the internal and external structure of plants, which in fact can be used as "testers" of their environment. The author presupposes that plants originated in a warmer and more humid climate than those found at the present time and colder or drier climates or seasons are "unfavorable" or less favorable from the point of view of plants, and the adaptations to them are more modern adaptations than the primitive body plan, and that the structure of plants does not necessarily reflect the distribution in which environmental conditions are most favorable to them, but their distribution in relation to whether they can compete with other plants present today. It does not take into account that at the time when plants originated they did not have variability such that their geographical regions were stratified.

The subdivisions (Raunkiaer 1903, republished in Raunkiaer 1934):

• I. Pherophites. Surviving buds are in geotropically negative stems projected in the air.
  • 1. Evergreen pherophites that don't cover their buds.
  • 2. Evergreen pherophites covering their buds.
  • 3. Deciduous pherophites covering their buds.
  • 4. Nanophanerophytes.
• II. Scams. Surviving buds are found in stems very close to the ground.
  • 5. Sufruticoa. The aerial stems are erect and geotropically negative, at the beginning of the unfavorable station die and the portion, of long variable, bearing the surviving buds.
  • 6. Passive bikes. The stems are persistent and geotropically negative but do not possess enough bra tissue to remain erect. They are therefore procumbent.
  • 7. Active bikes. The stems are persistent and transversally geotropic in relation to light? (and transversely geotropic in light), and for this reason they are procumbent.
  • 8. Plants in cushion (cushion plants).
• III. Hemicryptophytes. Surviving buds are on the ground surface.
  • 9. Protohemicriptophotes. From the base upwards the aerial stems have elongated interns and carry photosynthetic leaves, the leaves of the lower part are less developed than the others.
  • 10. Plants partially in rosette. The internudos near the base of the stem are short and is in this region where most and the biggest leaves of the foliage are originated. Upwards the internudes lengthen, the leaves are less, and the flowers originate.
  • 11. Plants in rosette (rosette plants). The stems are contracted at the base, where all the foliage of leaves originates. The elongate air stem carries only flowers.
• IV. Chryptophytes. Surviving buds are buried beneath the ground and at a distance from the surface that varies between species.
  • 12. Geocryptodies or geophytes.
    • a. Rhizome geophytes.
    • b. Bulb geophytes.
    • c. Tubercle Geophytes from the stem. (stem tuber geophytes)
    • d. Tube root geophytes. (root tuber geophytes)
  • 13. Limnocriptophytes or limnophytes (Lmnocriptophytes or limnophytes)marsh plants), editor's note: now called helophites.
  • 14. Hydrocryptophytes or hydrophites.
• V. Annual or Therophytes. Summer or favorable season plants.

Raunkiaer (1934:II), fragments:

p.5: "The requirements for plant life are all of equal importance, since none can be left aside, but when those requirements are used for the foundation of a division of the Earth In equiconditional regions, all requirements are far from having the same importance. Some, such as the amount of oxygen and carbon dioxide in the air, differ so little between locations that they have no significance when it comes to modeling life forms, so they cannot be used as characters to delimit equiconditional regions. Others, for example the chemical and physical nature of the soil, or the relations between plants and animals, and between plants themselves, vary so much even in the smallest districts that they cannot be used to delimit large equiconditional regions, but on the other hand they can be useful in the detailed analysis of the vegetation within these regions."

p.6: "The most important factors determining the environment that still need to be mentioned are humidity (moisture), water (here more specifically defined as precipitation) and temperature. Temperature regulates plant transpiration, therefore altering the significance of the amount of water present. The relationship between temperature and humidity is the factor that makes the greatest impression on vegetation in the current era. "Heat quâ heat" It certainly plays a very important role in the distribution of plants. Each species demands its own degree of heat (heat), and consequently each one occupies a corresponding geographical position. Megathermals or megaterms (note. "This and the terms that follow are used here to mean only the different heat demands (heat) of the plants. A. de Candolle, who first used them, included, although ultimately partially, demands for humidity (moisture) also".) they demand a lot of heat, and They will only grow where the temperature is relatively high throughout the year; They are consequently found only in the tropics. Mesothermics or mesotherms can withstand a considerably lower temperature for a longer or shorter period of the year, they can grow in tropical and subtropical regions, but it is only in the subtropical regions where they can conquer the competitors that demand a different degree of heat. Microthermics or microtherms are plants from temperate regions. They demand an even lower temperature, they do not need such a high temperature in summer, and they tolerate a much lower temperature in the winter. From this it does not necessarily follow, however, that the mentioned plants develop best under the available physical and chemical conditions. What is meant is that under these conditions they can prevail against competitors who demand a different degree of heat. A fourth group, hecystotherms or hecystotherms, comprise plants that belong to cold regions (cold). They have the lowest heat demand of all plants, will grow where summer is short, and are able to endure a long, very cold winter. Despite the fact that heat quâ heat is of such great importance in determining the distribution of plants, it is still impossible to use heat as a basis for delimiting equiconditional regions and characterizing these regions according to the lifespan of their plants (their plant life)."

p.7: "Of all the factors necessary for plant life, water is the one that, in very vast expanses of the Earth's surface, most closely approaches the status of a limiting factor. This is true even in regions where water appears to exist in sufficient quantity, as is the case in large stretches of the coldest regions of the planet, where at some times of the year the temperature is so low that plants cannot absorb the water.; In fact, they can die due to lack of available water while they are on water-saturated soil, perishing in what Schimper calls "physiological drought,", which has the same effect on plants that physical drought has on plants. warmer and drier regions."

p.8: "But this statement needs to be clarified. The important point is that environments not only differ in space but also in time. Conditions differ not only from locality to locality, but in the same locality they differ month to month. The seasons impose different conditions. Outside the tropics, where the climate is always hot and humid and therefore quite uniform and favorable throughout the year, all other regions have at least two seasons, one favorable and one unfavorable, or more correctly one more favorable and one less favorable. Those structural characters that enable plants to harmonize the demands of their vegetative organs with their environment are on the whole the characters that make the most obvious impression on the vegetation. From the nature of the case, however, the difference between the favorable seasons of two regions must be much less than the difference between their unfavorable seasons. This makes it exceedingly probable that those structural differences that allow plants to survive unfavorable seasons are greater than those that harmonize the same plants with favorable seasons. If we then want to use vegetation as a test of plant climate, to delimit equiconditional regions by means of the vegetation of those regions, we must, I think, do so by observing the peculiarities structural that allow plants to survive unfavorable seasons."

p.9: "As water in relation to temperature has the greatest significance in defining equiconditional areas, and as these two factors increase and decrease throughout the year, it becomes of great interest to make illustrations clear diagrams, like those shown in figures 1-6 [they are temperature and precipitation curves, and if it snows also marked, in each month of the year for different locations on the planet] of the relationship between these factors in given regions throughout the year." p.10: "Then each equiconditional region shows a characteristic figure that I will here designate as a hydrotherm figure, in which the most important environmental properties of the district are exhibited.'

• 

  Raunkiaer related the life forms of plants with the two most important environmental factors in defining their structure to a spatial scale that would allow the balloon to be divided into regions: temperature and precipitation, whose charts throughout the year in each locality he called hydrothermals. Here is something more complex than in the original publication. In the original publication mentions its combination in relation to the perspiration of plants, which today would be drawn as evapoperspiration graphics.

p.16-19: "In a constantly warm and humid climate plants can advance by developing new shoots, there is nothing in the environment that interrupts the continuous growth of the individual. In this climate we find mainly plants whose shoots project into the air, continuing their way of life from year to year in the manner of trees and shrubs. I will use the name phanerophyte (figure 7.1) to designate plants whose stems, which carry the buds that will form new branches, project freely into the air. If we examine the phanerophytes more closely we can divide them into subtypes according to whether their buds are more or less protected. We can differentiate, for example, evergreen phanerophytes without bud coverage, evergreen phanerophytes with bud coverage, and deciduous phanerophytes with bud coverage. The size of the plants has a very defined size in relation to humidity, so we can divide phanerophytes into mega-phanerophytes, meso-phanerophytes, micro-phanerophytes, and nano-phanerophytes.

Phanerophytes, especially the least protected of them, are the plants of those portions of the Earth that are the most climatically favored. In tropical regions that are constantly warm and constantly wet they form the bulk of the species, but as we leave the tropics and come to less and less favorable climates, to climates with a long, warm dry season, or climates with a severe winter, we find that phanerophytes decrease in proportion to the rest of the life forms. In these less favored localities we find only the best protected types of phanerophytes, especially those which in the unfavorable season lose their leaves and whose apical buds are protected by scales. Gradually, as we approach the limit at which phanerophytes cannot live, they become smaller and smaller in stature until we find only small shrubs and dwarf trees. Due to the low height of these plants they are not as exposed to the dangers of excessive transpiration as tall phanerophytes. In fact, in regions where snow falls in the winter they are often so low as to be protected by a snow cover, thus forming a transition to the second main type of life forms called the camephytes. Finally in the far north, in the highest regions of the high mountains, and in the dry steppes, phanerophytes disappear completely.

Caméphytes, the second main type, are characterized by having the surviving buds located close to the ground. This position may occur because the entire shoot remains flat on the ground (fig. 7.3), or because the distal portion of the shoot, which projects into the air, dies at the beginning of the unfavorable season, so that only the lower portion of the stem along with the surviving buds are kept behind (fig. 7.2). In cushion plants the surviving shoots are so densely packed and so short that the plants can be considered chamephytic.

The third type are the hemicryptophytes which have the surviving buds literally on the surface of the soil, protected by the soil itself and by the dead and dry portions of the plant (fig. 7.4). The aerial shoots, which bear leaves and flowers, survive for only a single vegetation period, and then die back to leave the part of the shoot lying on the ground and carrying the surviving buds. Most of our biennial and perennial grasses, and indeed the bulk of plants in the cold and temperate parts of the Earth, belong to this form of life, which may be subdivided according to whether the shoots are more or less modified. for life on the ground.

The cryptophytes, as the fourth type is called (fig. 7.5-9), are characterized by having their buds completely buried under the soil or under the bottom of the water. The depth to which the buds are buried varies in different species. This form of life is better protected against desiccation than hemicryptophytes, and is especially adapted to regions with a longer dry period, so the steppes are especially rich in cryptophytes. Many herbs with horizontal underground stems (horizontal root-stocks, fig. 7.5) and most bulbous and tuberous plants belong to this form of life (fig. 7.6). In the favorable season they send branches bearing leaves and flowers; In the dry period the plant is lost from sight, the buds are hidden at a greater or lesser depth under the soil.

The fourth form of life mentioned shows a series of progress in the same direction. As we travel away from the more favored portions of the Earth, which are characterized by phanerophytes, to climates with fewer elements? (less-element climates), we observe a tendency for the surviving buds to be carried, first near the soil surface (chamephytes), then on the soil surface (hemicryptophytes), and finally entirely buried under the soil or water (cryptophytes), where of course they are better protected from desiccation, which is their greatest danger.

The fifth form of life, the therophytes, comprise plants that complete their life cycle within a single favorable season, and remain dormant in seed form throughout unfavorable periods.. The shorter the period that these plants take to complete their life cycle, the more unfavorable the climate in which they are able to survive. Because these plants are able to complete their life cycle in a comparatively short period of time, often in the space of a few weeks, this form of life is the best protected of all. Therophytes disappear entirely during the unfavorable season of the year, during which they exist in the most protected form of all, that of the seed. They are particularly abundant in disadvantaged portions of the Earth, such as in steppes and deserts."