This group includes elements that are used as nutrients by only a limited number of plant species.  When high concentrations of an element, not commonly found in most plants, is seen in a particular species, it raises the possibility that the element is essential for that species.  The plants may use these for non-nutritional purposes.  It is thought that species where these elements are present may use them for protection against invading bacterii.  For example, Barium is found in brazil nuts; Aluminum in tea; Chromium, Nickel and Cobalt in gramineae; Silicon in rice and cucumbers.

BARIUM  (Ba) 137.33 Atomic Weight

(Essential Trace Element?)

Barium is not recognized as a plant nutrient, although it is found in certain plant species.  It constitutes 0.04% of the earth’s crust, totally in combinations with other mineral elements. Barium is widely used in the medical and manufacturing industries.  Though Barium minerals are very dense, barium itself is comparatively light.  Barium and all its mineral compounds that are soluble are toxic, so it is not known why some plant species survive with the levels of Barium present.