Most cultivated citrus taxa exhibit green first year twigs that become variously striate in subsequent growing seasons. The twigs of near relatives of citrus may be striate or sometimes mottled (e.g., Citropsis gilletiana and Murraya koenigii). The vast majority of taxa exhibit glabrous (hairless) twigs. Pubescent twigs are most widespread among the pummelos, but they may also be found in cultivars across a broad range of groups (including grapefruits, kumquat-like hybrids, limes, mandarin hybrids, and sour oranges, among others).
Cultivars differ in the extent to which they are armed, and the extent to which they retain their thorns, spines, or prickles. In general, thorniness is associated with juvenility. However, some cultivars, particularly lemons, bear more thorns into adulthood than others, such as the sweet oranges. Trifoliate orange (Poncirus trifoliata) and hybrids including this species frequently bear very stout thorns even on mature individuals. Although thorns are usually straight, a few trifoliate orange cultivars, such as Flying Dragon, exhibit recurved thorns.
Citrus ID Edition 2
October, 2011
idtools.org
