Indicator Plants of Soil: What They Are & How They Are Utilized

African Wood-Sorrel (Oxalis pes-caprae), Possible Indicator of Climate, in Olive Groove
African Wood-Sorrel (Oxalis pes-caprae), Possible Indicator of Climate, in Olive Groove

The Indicator Plants of Soil form an artificial sum of plant species, the presence of which in a soil area reveals some of its special characteristics.

The beginnings of this kind of categorization, which is generally related to Plant Indicators, should be sought in the beginnings of agriculture, and its longevity in the fact that they were an important aid for both farmers of the pre-scientific period and for the modern ones.

It is true that the value of plants as indicators not only of the condition of the soil but also of the wider environment in which they grow, in the age of science was questioned.

However, for several decades, and with the advocacy of many scientific studies, the questioning of their value has ceased to exist.

And well it ceased to exist, because among other things, observation, reasoning and verification are not a monopoly of the age of science. And in proportion, the producer of oranges did the Precision Agriculture, when he left some weeds in the orange grove, as indicators of the water status of the trees.

And at the right time he watered, with excellent results.

What and Which are the Indicator Plants of Soil

As Indicator Plants of Soil can be called those which with their presence indicate the condition of the specific soil area they occupy.

The condition of the soil, again, is mainly related to its physical, chemical and mechanical properties.

Therefore, by recognizing the Plants Indicators and knowing exactly what their presence indicates, one can get enough information about the type and properties of the observable soil.

Plants Indicators in theory can be any, but in practice they are mainly weeds. But if we take into account that weed is any plant that grows where it is not sown, then the practical is almost equivalent to the theoretical.

Indicator Plants of Soil: What They Are & How They Are Utilized

The Property of Plants to Be Taken as Indicators

The property of plants to be taken as indicators is related to their own existence. Every plant species, in order to be able to grow, must find the appropriate environment in terms of its biological – genetic heritage, so that with the effect and interaction between these two elements, it is possible to manifest by its occurance and behavior its characters.

For the most part, this takes place within the confines of a habitat, with more or less specific environmental conditions.

The growth of the individual or the plant community of the species within these limits, attributes to plants the quality of biological indicators of environmental factors that occur in the habitat.

Therefore, these plants, as biological indicators of environmental factors, refer not only to the soil, but also to the state of the atmosphere, water quality, etc.

Indicator Plants of Soil

The Reliability of Indicator Plants

The use of Indicator Plants is highly related to their reliability. This means that their utilization is directly proportional to their ability to provide the most accurate data possible on the environmental factors that affect within the boundaries of their plant communities.

And while the constant presence of some weeds in specific ecosystems could be a useful guide, for example to soil fertility, most weeds are not limited to a usable range and depth of conditions.

In fact, it could be emphatically stated here that the more adaptable individuals of a plant species are to certain factors in their growth environment, the less reliable they are – and vice versa.

This is easily understood, for example in the case of the agrochemical indicator of soil reaction, pH: if weeds adapt to a wide range of pH values, ie from acid soils to alkaline, then it is understandable that they can not be used as Indicator Plants of the specific soil factor.

Also, the anthropogenic intervention and the effects it can have on either urban or rural environments, regarding the presence or not of specific weeds or Indicator Plants, should not be overlooked.

The spraying of, for example, an agricultural area with non-selective herbicides and the presence of a single plant weed, which has developed resistance to these herbicides, must be taken seriously into account for the condition of the flora and the reliability of any Indicator Plants of the area.

Climatic - Soil Factors and Indicator Plants

Climatic and soil factors interact to create the right conditions for the emergence or prevalence of specific plant species of weeds in specific areas.

In fact, it could be said that the climate factor affects the width of the area of occurrence of Indicator Plants, while the soil factor is related to their local spread within this wider area.

What is particularly interesting is that the extreme areas offer the most reliable Indicator Plants, due to the marginal nature of the growing conditions of the weeds there.

Indicator Plants of Soil: What They Are & How They Are Utilized

The Common Nettle (Urtica dioica) is Another Herb which Acount as Indicator Plants of Soil with High Fertility
The Common Nettle (Urtica dioica) is Another Herb which Acount as Indicator Plants of Soil with High Fertility

The Utilization of Indicator Plants

The Indicator Plants are generally used to draw conclusions as to which land use is appropriate to be done in a certain or wider area.

Some Indicator Plants indicate agricultural exploitation, some others livestock, some others agroforestry or forestry.

The Indicator Plants of Soil, on the other hand, are utilized on the basis of the indications denoted by their presence regarding:

  • Soil health
  • The fertility of soil
  • The pH reaction (concentration of H + and OH- ions present in the soil solution)
  • Soil moisture levels
  • The amount of lighting that the ground receives
  • The density of the soil
  • The texture – mechanical composition of the soil
  • The porosity

Of these, the weakest plant indicator is that which refers to soil fertility. In this case, as a convincing number of studies have shown, only exceptionally and with many limitations, Indicator Plants can be used to determine the content of individual nutrient elements in soil.

Indicator Plants of Soil

Indicator Plants of Soil Fertility

Low Fertility Soils

Convolvulus arvensis (Bindweed, Creeping Jenny, European bindweed), Daucus carota (Wild Carrot, Bird’s Nest, Bishop’s Lace, Queen Anne’s Lace), Digitaria spp. (Crabgrass, Finger-Grass, Fonio), Hieracium aurantiacum (Orange Hawk Bit, Orange Hawkweed), Nardus stricta (Matgrass), Plantago spp. (Plantain, Broad-Leaved Plantain), Rumex acetosa (Sorrel, Garden Sorrel, Sour Dock), Rumex acetosella (Red Sheep Sorrel,Sheep’s Sorrel, Field Sorrel, Sour Weed), Trifolium repens (White Clover, Dutch Clover, Ladino Clover, Ladino), Verbascum phlomoides (Orange Mullein, Wooly Mullein)

High Fertility Soils

Amaranthus retroflexus (Redroot Amaranth, Common Amaranth, Common Tumbleweed, Pigweed), Galeopsis tetrahit (Common Hemp Nettle, Brittlestem Hempnettle), Stellaria media (Chickweed, Common Chickweed), Trifolium pratense (Red Clover, Purple Clover), Urtica dioica (Common Nettle, Stinging Nettle, Nettle Leaf)

Indicator Plants of Soil: What They Are & How They Are Utilized

Indicator Plants of Acid and Alkaline Soils

Acid Reaction Soils (pH <6.5-7)

Conium maculatum (Poison Hemlock, Deadly Hemlock, Poison Parsley), Fragaria vesca (Wild Strawberry, Woodland Strawberry, Alpine Strawberry, Carpathian Strawberry, European Strawberry), Galeopsis tetrahit (Common Hemp Nettle, Brittlestem Hempnettle), Ilex aquifolium (Common Holly, English Holly, European Holly, Prickly-Leaved Holly), Narcissus spp. (Daffodil, Narcissus, Jonquil), Stachys arvensis (Field Woundwort, Staggerweed), Raphanus raphanistrum (Wild Radish, White Charlock, Jointed Charlock), Rumex acetosa (Sorrel, Garden Sorrel, Sour Dock), Taraxacum officinalis (Common Dandelion, Dandelion, Blowball, Faceclock), Veronica officinalis (Heath Speedwell, Common Gypsyweed, Common Speedwell, Paul’s Betony)

Alkaline Reaction Soils (pH> 7-7.3)

Anthemis nobilis (Roman Chamomile, English Chamomile, Garden Chamomile, Ground Apple, Low Chamomile), Lepidium virginicum (Virginia pepperweed, Virginian Peppercress, Poorman Pepperweed, Peppergrass), Lithospermum officinale (European Stoneseed, Common Gromwell), Plantago lanceolata (Ribwort Plantain, Narrowleaf Plantain, English Plantain, Ribleaf, Lamb’s Tongue, Buckhorn), Plantago major (Broadleaf Plantain, White Man’s Foot, Greater Plantain, Rippleseed Plantain, Common Plantain), Rumex acetosella (Red Sheep Sorrel, Sheep’s Sorrel, Field Sorrel, Sour Weed), Silene latifolia (Bladder Campion, Bull Rattle)

Indicator Plants of Soil

Indicator Plants of Wet & Dry Soils

Wet Soils

Cerastium vulgatum (Mouse Ear Chickweed, Big Chickweed, Common Mouse Ear Chickweed), Cyperus esculentus (Yellow Nutsedge, Chufa, Tiger Nut, Atadwe, Earth Almond), Cyperus longus (Galingale), Cyperus rotundus (Nut Grass, Coco-Grass, Java Grass, Purple Nut Sedge, Purple Nutsedge, Red Nut Sedge), Echinochloa crus-galli (Barnyardgrass, Cockspur Grass, Barnyard Millet, Japanese Millet, Water Grass), Glechoma hederacea (Ground Ivy, Gill-Over-The-Ground, Creeping Charlie, Alehoof, Tunhoof, Catsfoot, Field Balm), Oxalis acetosella (Wood Sorrel, Common Wood Sorrel), Poa annua (Annual Bluegrass, Plains Bluegrass,Walkgrass), Stellaria media (Chickweed, Common Chickweed), Solidago graminifolia (Grass Leaved Goldenrod)

Dry Soils

Achillea millefolium (Yarrow, Devil’s Nettle, Dog Daisy, Dog Fennel, Milfoil, Soldier’s Woundwort, Thousandleaf, Westen Yarrow), Anthemis tinctoria (Golden Marguerite, Yellow Chamomile, Oxeye Chamomile), Euphorbia dendroides (Tree Spurge), Euphorbia maculata (Spotted Spurge, Prostrate Spurge), Ornithopus perpusillus (Little White Bird’s Foot, Bird’s Foot), Oxalis stricta (Common Yellow Woodsorrel, Common Yellow Oxalis, Sour Grass, Shamrock, Sleeping Beauty), Thymus pulegioides (Broad Leaved Thyme, Lemon Thyme)

Indicator Plants of Soil: What They Are & How They Are Utilized

Indicator Plants of Soil Type

Light Soils (Sandy)

Adonis aestivalis (Poison Hemlock, Summer Adonis, Summer Pheasant’s Eye), Calligonum polygonoides (Phog), Casuarina equisetifolia (Australian Pine Tree, Common Ironwood, Horsetail Casuarina, Beach She-Oak, Coast She-Oak), Citrullus colocynthis (Colocynth, Bitter Apple, Bitter Cucumber), Gonsolida regalis (Forking Larkspur, Rocket-larkspur, Field larkspur), Ipomoea pes-caprae (Bayhops, Beach Morning Glory, Goat’s Foot), Lycium barbarum (Chinese Wolfberry, Chinese Boxthorn, Himalayan Goji, Tibetan Goji), Papaver argemone (Prickly Poppy, Long Pricklyhead Poppy), Plantago amplexicaulis (Ispaghula), Verbascum thapsus (Great Mullein, Common Mullein, Aaron’s Rod, Flannel Plant), Ornithopus perpusillus (Little White Bird’s Foot, Birdsfoot), Stellaria media (Chickweed, Common Chickweed), Trifolium arvense (Rabbitfoot Clover, Hare’s-Foot Clover, Stone Clover, Oldfield Clover)

Medium Soils (Loamy)

Colchicum autumnale (Autumn Crocus, Meadow Saffron, Naked Ladies), Matricaria chamomilla (German Chamomile, Hungarian Chamomile, Wild Chamomile, Blue Chamomile), Daucus carota (Wild Carrot, Bird’s Nest, Bishop’s Lace, Queen Anne’s Lace), Tussilago farfara (Assfoot, Coltsfoot, Coughwort), Veronica persica (Persian Speedwell, Large Field Speedwell, Bird’s-Eye, Winter Speedwell)

Heavy Soils (Clayey)

Cichorium intybus (Common Chicory, Succory, Chickory, Blue Sailors, Coffeeweed), Elymus repens, syn. Agropyron repens (Common Couch, Twitch, Quick Grass, Quitch Grass), Imperata cylindrica (Cogongrass, Blady Grass, Thatch Grass), Urtica dioica (Common Nettle, Stinging Nettle, Nettle Leaf), Taraxacum officinale (Common Dandelion, Dandelion, Blowball, Faceclock), Vetiveria zizanioides, syn. Chrysopogon zizanioides (Vetiver)

Compacted Soils

Alopecurus pratensis (Meadow Foxtail, Field Meadow Foxtail), Allium vineale (Wild Garlic, Onion Grass, Crow Garlic), Centaurea scabiosa (Greater Knapweed, Black Knapweed, Black Top, Churls Head), Cerastium virgatum (Mouse Ear Chickweed, Clammy Chickweed), Cichorium intybus (Common Chicory, Succory, Chickory, Blue Sailors, Coffeeweed), Digitaria spp. (Crabgrass, Finger-Grass, Fonio), Eleusine indica (Indian Goosegrass, Yard-Grass, Goosegrass, Wiregrass, Crowfootgrass), Equisetum arvense (Field Horsetail, Common Horsetail), Euphorbia maculata (Spotted Spurge, Prostrate Spurge), Imperata cylindrica (Cogongrass, Blady Grass, Thatch Grass), Juncus tenuis (Slender Rush, Slender Yard Rush, Wiregrass, Field Rush), Mentha arvensis (Wild Mint, European Corn Mint, Wild Mint, Field Mint, Japanese Peppermint), Mercurialis annua (Annual Mercury, French Mercury), Potentilla anserina (Silverweed, Common Silverweed, Silver Cinquefoil), Plantago major (Broadleaf Plantain, White Man’s Foot, Greater Plantain, Rippleseed Plantain, Common Plantain), Poa annua (Annual Bluegrass, Plains Bluegrass,Walkgrass), Polygonum aviculare (Prostrate Knotweed, Common Knotgrass), Ranunculus repens (Creeping Buttercup,  Creeping Crowfoot), Stellaria media (Chickweed, Common Chickweed), Taraxacum officinale (Common Dandelion, Dandelion, Blowball, Faceclock), Trifolium repens (White Clover, Dutch Clover, Ladino Clover, Ladino), Veronica arvensis (Corn Speedwell, Wall Speedwell, Common Speedwell, Rock Speedwell), Vetiveria zizanioides, syn. Chrysopogon zizanioides (Vetiver)

Indicator Plants of Soil: What They Are & How They Are Utilized

References

The References of the article entitled Indicator Plants of Soil: What They Are & How They Are Utilized are presented by the late Filio Pyrgaki (Φιλιώ Πυργάκη, October 11, 1939 – July 17, 2021) with the song Βουνά Για Χαμηλώσετε (Mountains Let Be Lower) – accompanied by George Magga (Γιώργος Μάγγας) on clarinet.

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Indicator Plants of Soil: What They Are & How They Are Utilized

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