The ecological environment of the Datura species.
Vast areas of the South-Western USA and Mexico are covered by deserts. These areas are characterized by low levels of rainfalls and day temperatures, which easily exceed 40*C.
In fact, the sand and the rocks can be so hot, that you will burn your feet severely when walking barefooted. Usually, the night temperatures are very low. In some desert areas, nightly freezes frequently occur during winter.
In these dry areas, water is essential to survival. Apart from the short, and often heavy seasonal rainfalls, rivers, and creeks cutting through these landscapes are the only water supplies available to animal and plant life.
In spite of these often harsh environmental conditions, many desert plants are able to persist for several
decades. The enormous columnar cacti are able to store several tons of water in their trunks during a heavy shower. Smaller shrubs and trees survive by extending their root systems deep into the underground or by settling in favorable spots in respect of nutrition and water.
During the rainy season, millions of short-lived annuals become visible above the sand. In the dry season, you utterly fail to notice the presence of their seeds scattered all over
the sandy flats, but when the wet season occurs, these seeds germinate and grow into small herbaceous plants. When in flower, the desert floor seems to be covered by a magical colorful carpet. In a short time, these plants grow out, flowers and throw their seeds, after which they dry out and vanishes before our eyes.
Another group of vegetation found on dry land has adapted otherwise to the desert environment. The plant species in this group have no large organs
for water storage, as has the cacti. Neither is the life circle short enough to be concluded when the surface of the soil dries out. Although tender from the hands of nature, these plants appreciate sunlight and heat. Compared to the majority of desert plants, the present group has high demands of the level of soil moisteners and of nutrition. These plants are found in the vegetation belts of river banks, creeks, and flood plains. Here among the thousand other interesting plant species, you may catch a glimpse of a group of meter-high, rank-smelling herbs carrying large leaves, conspicuous, trumpet-shaped flowers, and round fruits covered by long, slender spines.
These are the Daturas.
Distribution in general
Today the Datura species are distributed throughout the world. Even though, that all species – including the “Asiatic” D. metel. and the “Australian” D. leichhardtii (Symon, Haegi, 1991) – are natural inhabitants of the great deserts, these can also be found in totally different environments and in unexpected parts of our world.
More Datura species have been naturalized on the other side of our green planet. These species occur in sporadic populations in large parts of Scandinavia, Europe, Asia, Russia, The Middle East, and in limited populations on semi-dry land scattered over Africa and Australia.
Datura species are frequently found in semi-dry deserts in the most favorable places in regard to water supply and nutritive soils. In spite of the fact, that there exist exceptions with some species, where populations have been found growing under very poor conditions, the Datura`s are typically an integrated part of the vegetation belts of the river banks, flood plains, and dry beds.
The Datura`s can frequently be found in spots, where the soil is able to maintain its moistures in a considerable period of time. The typical soils are sand, gravel, or alluvial clay.
In general, most desert soil types are largely composed of minerals. Tests will usually reveal high contents of calcium and magnesium relative to other soil types, whereas the content of organic matter is low to such an extent, that in many elevated areas it is hardly detectable to the naked eye.
Not all desert areas are wasteland in the meaning, that they are barren. There are rather fertile and nutritive soil types in the deserts too. The underlying layers in these soils are composed of sand, gravel, or clay mixed with stones of various sizes. The surface layers contain a high percentage of organic matter.
In the moist periods, the decomposition process happens rather quickly. But the organic layers are continuously supplied remains of dead animals and insects together with withered and decaying plant materials.
These matters originate from the vast elevated sandy areas. During the heavy rainfalls, these remains are washed away by sheet flood erosion and deposited in the depressions as for instance on the flood plains and in the dry beds.
Morphology in relation to habitat
The Datura`s are adapted to a xeric environment, however, it would be an error to regard them as xerophytes. In many aspects of morphology, it would be more correct to consider them to be mesophytes.
Only D. inoxia, D. meteloides and D. wrightii has a single morphological character in common with some xerophytes: the swollen and enlarged stem basis situated above the taproot.
This character enables these species to survive a period of severe drought, that would put to misery any other Datura species. The plant parts above the sand simply die back to the roots and start shooting anew, when the conditions are favorable.
The morphological expressions, which characterize the herbaceous Datura species, are a well-developed tap root system, which is able to extend to 1.5 m. or more into the underlying soil layers.
Stem and branches are slender and tend to become hollow with age. In older specimens, the stem basis tends to develop the same kind of woodiness as can be found in the species of Sect. Brugmansia. This especially applies to D. inoxia, D. meteloides and D. wrightii, but the remaining species also forms, what could be determined as “secondary woodiness”.
The leaf mass is considerable both in regard to leaf number and leaf size. In some species, the leaf is covered by soft hairs to prevent excessive evaporation. In other species, the leaf has fairly cut margins to allow the wind to slip through.
The tube-formed calyx protects the undeveloped flower bud against insect attack and prevents it from drying out.
The trumpet-shaped flowers not only arouse the interest of night moths, they also serve as a platform for these nocturnal beings, while sucking nectar from the corolla tube.
The corollas are followed by spiny fruits of a size of a wall nut. The spines prevent larger animals from biting the fruits. The seed coat protects the embryo from being eaten by mammals or insects. When dry, the seed coat enables the seeds to travel to some distance by the aid of wind or water.
Adaptation to semi-arid environment
The Datura species are frequently growing in a semi-dry desert environment, which is characterized through a low level of rainfall more or less confined to be of seasonal occurrence. As it can be verified from a cultural situation, height and total plant mass are dependent on the number of soil moistures available to the root system during plant growth.
In order to resist the ecological pressures, the Datura`s have adapted successfully to the semi-arid environment by the speed of germination, rapid growth, early flowering, and early maturing of fruits and seeds. When the environmental factors are uttermost favorable, these plants will produce several hundred flowers succeeded by as many fruits and produce them continuously. The only factors preventing them from doing this are the dangers of drought or nightly frost.
In a cultural context, D. stramonium (DATU-03 – DATU-06 – DATU-10), D. meteloides (DATU-44 – DATU-45 – DATU-R-45 – DATU-48 – DATU-50 – DATU-72), and D. leichhardtii (DATU-37 – DATU-110) are able to continue the production of flowers and fruits for more that two seasons and there is no doubt, that D. meteloides (DATU-49) and D. wrightii (DATU-82) can attain a very high age.
Life circle in relation to the environment
In contrary to the strict summer annual plant species found on semi-arid land, the Datura`s are not “from the hands of nature” to a short, annual life. Whereas a fairly large group of summer annuals are capable of completing a full life circle within a period of a few months, the Datura´s are characterized through a much longer duration.
At the present time, many Datura species are in fact regarded as summer annuals or annuals. But here one must ask, whether this determination is based on the examination of plants interacting with the environmental factors present in habitat – even in a specific habitat – or if it is based on examinations of specimens grown out under the best possible conditions in regard to temperature, soil moistures and sufficient supply of nutritive elements?
In case that life circle is determined according to plant behavior in habitat, that gives rise to the question of exactly which habitat?
A specimen of D. tatula growing in a habitat in Colorado could easily – depending on the climatic conditions in the year it was exanimate – be determined as a summer-annual, whereas another specimen of this species growing in a valley close to a permanent river in the inner of Mexico could be determined as strictly annual to biennial.
As it will be seen clearly, the definition of longevity is relative to a specific narrow confined geographical location, not to the species as a whole.
This fact also offers an explanation to the question, why a given Datura species in one flora is described as a summer annual and in another flora is described as annual or perennial.
Ecologically disturbed areas
In the past three hundred years, vast desert areas were turned into, what is determined as ecologically disturbed areas. Tremendous amounts of land were cleared to give space for field crops, grassland, mining industry, and transportation roads. Flood plains were turned under the plow and also many rivers, and the ecological system dependent on these rivers was partly destroyed due to the building of dams, artificial canals, and irrigation ditches.
Large and irreplaceable plant populations in the vegetation belts of the lower rivers were destroyed due to insufficient water supplies. New and sometimes almost identical vegetation belts were, however, soon established along with the dams, canals, and ditches.
These artificially constructed waterways is a true picture of the catastrophes created by a disturbed ecological system but are also a confirmation of the fact, that the destruction contains the seeds of a new way of life. These sites have provided the Datura`s, as well as many other plant species, with an environment containing extraordinarily favorable conditions for the establishment of permanent populations.
Especially the water canals and ditches, where the water level is plenty all year. Here the Datura species have optimal conditions both for seed establishment and for long-lasting growth.
A similar situation characterizes the life of the roadside Daturas. Their root system is effectively kept moist by the water run-off from the roads.