Malus rockii Rehder

Description

Malus rockii is a tree of 8 to 10 m with drooping branches. Its leaves are elliptic to oblong-ovate, 6–12 cm long and hairy on the veins beneath. The flowers are 2.5–3 cm across with white petals; the fruit is red, egg-shaped or roundish and 1–1.5 cm across, and its sepals fall before it ripens. In China it flowers in May and June and fruits in September. Plants with 34 and 51 chromosomes have been counted¹.

It is close to the Siberian crab apple, from which Rehder distinguished it by its much hairier leaf undersides and its rather late-falling calyx².

Range and habitat

It grows in mixed forest in valleys at 2,400–3,800 m in south-western Sichuan, south-eastern Tibet and north-western Yunnan, and in Bhutan¹; the IUCN Red List adds Guizhou³, and Plants of the World Online extends its range into central China⁴. The IUCN Red List assessed it in 2017 as Least Concern³.

History

Rehder described it in 1933 from specimens collected in Yunnan in 1922 and 1923 by the plant collector Joseph Rock, and Rock’s seed of 1932 brought it into cultivation at the Arnold Arboretum. The trees grown there from that seed are tetraploid, and so presumably set seed without fertilisation. In gardens it is a small, disease-resistant tree with white flowers from pink buds and bright red, long-lasting fruit².

Where the sources disagree

• What it is. The Flora of China treats it as a species that includes the Bhutanese Malus baccata var. himalaica¹, but Keith Rushforth considers the two different. Taylor treated the cultivated plant as a form of Malus sikkimensis, as the Arnold Arboretum’s catalogue still does, and the Royal Botanic Garden Edinburgh lists it simply as a synonym of Malus baccata². Plants of the World Online and the 2022 revision accept it as a species^4,5.