This interesting species was described in 1980 (Notes Roy. Bot. Gard. Edin., Vol. 39, pp. 129-36). It is intermediate between P. spinulosa and P. brachytyla, approaching the former in its open crown and pendulous ultimate branches, but with shorter, broader and more flattened leaves, snowy white beneath; it also differs from that species in its darker, scarcely glossy shoots and its almost sessile leaf-cushions (pulvini), which in P. spinulosa are long and narrow. From P. brachytyla it differs in habit, the more radial arrangement of the longer and narrower leaves, which are also more parallel-sided and less pungent.
P. farreri was discovered by Reginald Farrer in the Feng-shui-ling valley of upper Burma near the frontier with Yunnan, and was described from a tree at Exbury, Hants, raised from the seeds he sent (Farrer 1435) and from specimens collected by C. W. D. Kermode in the type-locality. Geographically it lies nearer to P. brachytyla, which occurs in Yunnan, and is remote from P. spinulosa, which so far as is known does not extend as far east as Burma.
The tree of P. farreri at Exbury was planted in 1921, and is about 60 ft high and 5 ft in girth. A coning branch is figured in Quarterly Journal of Forestry, Vol. 79, p. 13 (1979).