The date is established by the relationship between this letter and the letter to Asa Gray, 20 December 1876.

In his taxonomic study, Enumeratio plantarum Zeylaniæ (Enumeration of the plants of Ceylon; Thwaites 1858–64, 5: 54, 205), George Henry Kendrick Thwaites used the terms stylosa and staminea to describe the different floral forms of Sethia obtusifolia (a synonym of Erythroxylum obtusifolium), Sethia acuminata (a synonym of Erythroxylum moonii), and Limnanthemum indicum (a synonym of Nymphoides indica, water snowflake). In his description of Sethia obtusifolia, Thwaites remarked that although he initially considered that the two forms might be different species, he later concluded that they foreshadowed a ‘dioecious character’ (ibid., p. 54). CD included Thwaites’s description of Limnanthemum indicum and the species of Sethia in Forms of flowers, pp. 116, 122.