Carl Wilhelm von Nägeli: Achillea species and lime (1865)
(quoted in: Plant-geography upon a physiological basis. pp. 105-106 (1903) by Schimper, et al.)

Achillea moschata excludes A. atrata from a silicious soil and is itself excluded by the latter from a calcareous soil. On the other hand, either of them grows equally well in the company of A. Millefolium. Evidently the two first-mentioned plants, as they are externally extremely alike, make analogous demands on the environment. A. Millefolium, however, which systematically is further removed from either, does not compete with them, because it is dependent on other conditions of existence. If either of the two species be absent, the other becomes indifferent as regards its choice of soil.

1. Achillea atrata. Calciphilous. 2. Achillea moschata. Calciphobous.

In Bernina-Heuthal (Upper Engadine), A. moschata, A. atrata, and A. Millefolium, all abound; A. moschata and A. Millefolium on slate, A. atrata and A. Millefolium on lime. Wherever the slate passes into limestone, A. moschata at once stops and A. atrata begins. Both species are here therefore strictly confined to one soil; and this I have also observed in several places in Bündten, where the two species occur. If one of the species be absent, the other becomes indifferent as regards its choice of soil. A. atrata then inhabits both lime and slate indifferently; the same fact also applies to A. moschata: although, as it appears, this species does not thrive so well on limestone as the other does on slate, yet, besides occurring on the primary mountains, it is also found on pronounced lime formations, along with the usual characteristic vegetation. In Bernina-Heuthal, I found in the midst of the slate that was stocked with A. moschata a large fallen block of limestone with a layer of soil on it hardly an inch thick. A colony of A. moschata had settled on it, as there all competition with A. atrata was excluded.

1865 Ueber die Bedingungen des Vorkommens von Arten ... Sitzungsberichte der bayrischen Akademie 1: 367