Bucklandiella angustissima Bednarek-Ochyra et Ochyra is described as a new species. It is known in Australasia from the southern cool-temperate zone of the South Island of New Zealand and its offshore islands including the Auckland and Campbell Islands, as well as subantarctic Macquarie Island, and in South America from the northern Andes of Ecuador. The new species belongs to Bucklandiella Roiv. sect. Emersae (Bednarek-Ochyra) Bednarek-Ochyra et Ochyra and is allied to Australasian B. emersa (Müll. Hal.) Bednarek-Ochyra et Ochyra. It is a saxicole readily distinguished from all its congeners in having very small, subglobose to ovoid or obloid capsules, 0.5-0.8 mm long, on fairly stout and very short setae, only 0.8-1.2 mm. These are the smallest capsules and the shortest setae in the large genus Bucklandiella. Additionally, the species has very short peristome teeth, 200-220 m long, and a very narrow costa, 40-60 m wide, with only two enlarged adaxial epidermal cells throughout its entire length. The taxonomic status of Racomitrium crispipilum (Taylor) A. Jaeger var. brevifolium Thér., which is known only in sterile condition from a single altimontane site in Ecuador, is briefly assessed and this variety is considered to be identical to Bucklandiella angustissima. Five new combinations are made: Bucklandiella subsect. Andicola (Bednarek-Ochyra) Bednarek-Ochyra et Ochyra, B. subsect. Depressae (Bednarek-Ochyra) Bednarek-Ochyra et Ochyra, B. depressa (Lesq.) Bednarek-Ochyra et Ochyra, B. dichelymoides (Herzog) Bednarek-Ochyra et Ochyra, and B. subcrispipila (Müll. Hal.) Bednarek-Ochyra et Ochyra. The latter name is neotypified.