Architecture of a clonal population of Muehlenbeckia astonii Petrie (Polygonaceae), a divaricating shrub endemic to New Zealand

Abstract

Muehlenbeckia astonii Petrie is a compact, divaricating shrub. It produces both orthotopic and plagiotropic shoots but after a period of time the orthotopic shoots revert to a plagiotropic form. Orthotropic shoots differ from plagiotropic ones in that the internodes are longer, the shoots more erect and much straighter for the first 10-15 intemodes. A clonal population of two-year-old cuttings, taken from a female plant, was grown outdoors in pots. Those cuttings supplied with a balanced nutrient solution were more vigorous and produced more second-order orthotropic shoots than those not provided with nutrient. However, nutrient level did not affect the ultimate divaricating nature of the shoots. The vigour of the shoots varied. Generally, a shoot grew vigorously for the first season producing many other shoots of higher orders; then extension of the second-order axis ceased and further growth was restricted to the higher-order laterals. Most of the growth was carried out by shoots initiated in the current growing season. To a large extent the number and vigour of the orthotropic shoots determined the overall form of the plants. These shoots sometimes arose below or close to ground level but often in older plants also developed as laterals on second- or third-order shoots some distance above the ground. Plagiotropic shoots did not increase the overall height of the shrub to any great extent, but orthotropic ones were important in that they placed shoots at a higher elevation and thus increased the volume of space occupied by the plant.

Keywords:

• Muehlenbeckia astonii
• divaricating shrub
• branching
• growth form
• response to nutrient
• Polygonaceae