Calcium (Ca2+) is an essential plant nutrient that plays a key role in plant growth and development and an essential second messenger that controls a variety of cellular functions. It also plays a role in cellular regulation of plant cell signaling. Plants rely on the unique properties of Ca2+ for a range of structural, enzymatic, and signaling functions. Of the many nutrients essential for normal growth and development of plants, Ca2+ occupies a unique position both chemically and functionally. Soils vary widely in their Ca2+ content and therefore, adaptations shown by plants, mainly to this factor, have led to the emergence of two very distinct ecological divisions termed as calcicoles (grow on calcareous soils) and calcifuges (grow on acidic soils). As excess Ca2+ is toxic to plants the sequestering of incoming Ca2+ as Ca2+ oxalate in epidermal trichomes has been studied in calcicoles from high Ca2+ enriched environments (calcareous soils). However, much less is known about the molecular basis of adaptation to this ecological phenomenon as well as the morphological adaptation patterns of calcicoles and calcifuges in response to varied levels of rhizospheric Ca2+. In this study, six ecotypes of A. thaliana, comprising two putative wild calcifuges (Glenisla and Penicuik), two putative wild calcicoles (Halifax and Elland) collected from varyingly calcareous regions around UK, and two lab grown ecotypes (Col-4 and Cal-0) were subjected to varied concentrations of Ca2+ stress under invitro conditions and a difference in growth and morphology of these ecotypes was measured. Also, DNA microarray analysis was utilized to detect genes that are regulated by Ca2+. A differed pattern in the root growth was observed in all the ecotypes at varied external Ca2+ application ranging from 0 mM to 30 mM. The primary root structure and growth differed markedly in Glenisla plants grown at 30 mM Ca2+. TUNEL assay determined the occurrence of apoptosis in the same Glenisla roots. Also, ten repressed Calcium-responsive genes in Cal-0 (Cal-CRGs) at high Ca2+ were investigated in all the six ecotypes using Real time RT-PCR, demonstrating their differed expression patterns in putative calcicoles to putative calcifuges. Analysis of SALK T-DNA knockout Cal-CRG5 and Cal-CRG17 lines, revealed the potential role of repression of these genes in rhizospheric Ca2+ tolerance.