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Eucalyptus trees draw up gold particles from 35-metre-deep deposits with their deep-growing roots, depositing it in their leaves and branches, Australian scientists reported 22 October 2013

Geobotanical Prospecting: Plants Reveal Riches



Bitumen near the Caspian Sea and in California; cobalt, iron and nickel in Russia; copper and nickel in central and southern Africa; copper and silver in Montana; gold in Australia; tin and tungsten in England – all have been revealed by indicator plants.
Writings from 5th-century B.C. China reveal what was undoubtedly a far older practice. Observations were recorded accurately but the colloquial names used for the indicator plants have resulted in considerable confusion. But by medieval times, it was recorded that Scandinavian miners searching for copper used Lychnis alpina as an indicator. Today, at least 85 species are believed to mark sites that are likely to be enriched in a particular element or mineral. Plants belonging to the Leguminosae, Caryophyllaceae and Labiatae are particularly prone to act as indicators. Some will be familiar to gardeners. For example, the florist’s hydrangea, H. macrophylla, remains resolutely pink – unless exposed to aluminum sulfate. Less welcome might be the news that the blue stamens of Western Spiderwort, Tradescantia sp., change to pink when radiation is present in the environment. Eucalyptus trees draw up gold particles from 35-metre-deep deposits with their deep-growing roots, depositing it in their leaves and branches, Australian scientists reported 22 October 2013 in Nature Communications. The team suggested that eucalyptus trees might offer a new way to locate hidden treasure. However, raking up fallen leaves in the hopes of sustaining a golden future is unlikely to be fulfilled. At about one-fifth the diameter of a human hair, the “nuggets” are invisible to the naked eye. How about diamonds then? Earlier this year, Geologist Stephen Haggerty discovered a thorny, palm-like plant in Liberia, West Africa. Pandanus candelabrum appear to grow on top of kimberlite pipes – columns of volcanic rock hundreds of metres across that extend deep into the Earth, left by ancient eruptions that exhumed diamonds for the mantle, writes Eric Hand in Science. Haggerty suspects that the plant has adapted to kimberlite soils, which are rich in magnesium, potassium and phosphorus. “It sounds like a very good fertilizer, which it is,” Haggerty told Science. He has published the discovery in the June-July issue of Economic Geology.

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A brief selection of indicator plants includes:
  • Aluminum: Hydrangea macrophylla
  • Bromine: Allium cepa
  • Chromium: Nicotiana tabacum
  • Cobalt: Crotalaria cobalticola; Nyassa sylvatica; Andropigan viginicus
  • Copper: Eschscholtzia mexicana (Mexican golden poppy); Hyptis suaveolens; Haumaniastrum katangnse
  • Diamond: Pandanus candelabrum
  • Gold: Equisetum arvense, E. confusa (horsetail); Eucalyptus spp.; Artemisia spp. (Sagebrush); Atriplex spp. (Saltbrush)
  • Nickel: Alyssum bertoloni; Berkheya coddii
  • Selenium: Astragalus albulus, A. argilosus
  • Silver: Eriogonum ovalifolium (buckwheat family); Lonicera confusa
  • Sulfur: Eriogonum inflatum; Oenothera caespitosa
  • Uranium: Astragalus spp.; Aster venusta; Juniperus spp.
  • Zinc: Viola calaminaria; Philadelphus spp. Ambrosia artenaisoofolia; Thlaspi spp. (pennycress)
So what is the catch? First, knowledge of botany is necessary. And while mineral deposits might be present, climate or other conditions prevent the particular indicator plants from surviving at that location. Lastly, as in the case of the extraction of gold by Eucalyptus, a laboratory analysis may be required to confirm its presence.


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Wes Porter -- Bio and Archives

Wes Porter is a horticultural consultant and writer based in Toronto. Wes has over 40 years of experience in both temperate and tropical horticulture from three continents.


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