Buddleja caryopteridifolia W.W. Sm.

There is some confusion around the early collections of this species. It was first described from a flowering specimen collected by Forrest in Yunnan in 1913 (Smith 1914), but no seed was introduced on that occasion. The plants once cultivated under the name B. caryopteridifolia derive from seed sent by Forrest during his 1921–23 expedition, raised at the Royal Botanic Garden Edinburgh and at Highdown. Later, Cotton (1947) named the Highdown plant B. sterniana, in honour of Sir Frederick Stern, now sunk as a synonym of B. crispa. Bean (1976) considered it unlikely the authentic B. caryopteridifolia was ever in cultivation, although Fletcher (1954) describes a cultivated plant that could be B. caryopteridifolia. The current author believes the plants now labelled as B. caryopteridifolia in the horticultural trade and in gardens represent an unidentified hybrid of B. alternifolia, possibly B. × wardii or a similar hybrid, whose foliage can be opposite, sub-opposite, and alternate on the same plant. The authentic B. caryopteridifolia always has opposite leaves and does not appear to have survived in ex situ collections.

Bearing some similarity to a small or immature B. crispa (of the type previously described as B. sterniana), B. caryopteridifolia typically has very small inflorescences of few pale lilac-pink or grey-lavender flowers, densely tomentose stems, and small glaucous leaves with a crenate to shallowly lobed margins. B. caryopteridifolia is autumn flowering in contrast to all types of B. crispa, which flower in spring to early summer. It can be distinguished in the field from B. crispa by its smaller inflorescences, longer bracts, significantly smaller leaves, and more compact habit. The chemical constituents of the flower-scent have been shown to be different in the two species; genetic studies have likewise confirmed they are distinct (Zhang 2014).