Raspberry growth habit and morphology

Canes and foliage

The main stem of the raspberry is called a cane. Canes grow one year and fruit the next, but there are also primocane varieties which fruit in the first year. The biennial growth cycle of raspberry stems begins when an axillary bud from below soil level develops and elongation of the internodes carries the growing point, protected by leaf scales, to the soil surface. At the surface, leaves expand to form a tight rosette around the growing point. Elongation of the shoot starts in spring and continues until autumn, by which time the shoot will have attained a height of 2 to 3 m. In red raspberries (R. idaeus L.), shortening days and falling temperatures in late summer cause shoot elongation to cease and dormancy to set in. This is a gradual process extending over several weeks and once a stage of complete dormancy is reached it is not readily reversible. Black raspberries (R. occidentalis L.) or purple raspberries (hybrids between red and black raspberries) and most blackberries differ from red raspberries both in time when dormancy begins and intensity of dormancy attained. In these fruits, growth continues well into autumn. The initiation of flower buds usually starts at the same time as the canes begin to acquire dormancy. In the spring of the second year, vegetative primocanes become fruiting canes.

Flowers and fruit

Small (0.5-1.5 cm), white to pink flowers are initiated in the second year of planting. The gynoecium consists of 60-80 ovaries, each of which develops into a drupelet. There are 60-90 stamens. Raspberries produce copious amount of nectar and attract bees. The flowers of Rubus are structurally rather similar to those of strawberries, with five sepals, five petals, a very short hypanthium, many stamens, and an apocarpous gynoecium of many carpels on a cone-like receptacle. Raspberries are an aggregate fruit, composed of individual drupelets, held together by almost invisible hairs. The one-seeded drupelets are set together on a small conical core (Jennings 1988). In Rubus each carpel will develop into a small drupelet, with the mesocarp becoming fleshy and the endorcarp becoming hard and forming a tiny pit that encloses a single seed. Each drupelet usually has a single seed, though a few have two. Fruiting begins in the second year of planting and in favourable conditions plantations can continue to fruit for more than 15 years. Fruit development occurs rapidly, taking only 30 - 36 days for most raspberry cultivars.

References

Jennings DL (1988) Raspberries and blackberries: their breeding, diseases and growth. London: Academic Press, 230 pp.