Clonal segmentation - The development of physiological independence withinstolons of Glechoma hederacea L-(Lamiaceae)

The youngest parts of clonal plants benefit from substantial physiological support from older parts, but the extent to which this physiological depend ence persists through time is poorly understood. The development of autonom y among connected subunits was therefore analysed in the clonal species Gle choma hederacea. The stolons of a series of clonal fragments with differing numbers of primary ramets were severed at a fixed point relative to the fo ur oldest primary ramets. The subsequent growth of both parts of the severe d fragments was compared with that of a series of intact fragments. The growth of apical stolon portions that included five or more rooted prim ary ramets at the time of severing was unaffected by severing. Apical porti ons with three or fewer rooted ramets at the time of severing produced fewe r new primary ramets than equivalent parts of intact fragments, while apica l portions with four or fewer rooted ramets produced less above-ground mass than equivalent apical portions of intact clonal fragments. Basal portions of clonal fragments severed when there were one or two rooted ramets in th e apical portion produced more secondary ramet mass than equivalent parts o f intact fragments. The gain in mass of secondary ramets in the basal porti ons of severed fragments matched the reduction in mass of secondary ramets in the apical portions. However, severing caused an overall loss of mass wh en apical portions had three or fewer rooted ramets at the time of severing , because the mass of primary ramets in basal portions did not increase fol lowing severing. Severing had little impact on the allometry of the apical portions. The relationship between mass in secondary ramets and mass in pri mary ramets was similar in the apical portions of severed and intact clonal fragments. None of the severing treatments increased the total mass of sec ondary ramets, suggesting that apical dominance in this species only affect s branches very close to the apex. These observations, combined with existing knowledge of vascular architectu re in G. hederacea, demonstrate that, whether or not physical connections p ersist between ramets, growing stolons rapidly develop into physiologically autonomous segments. This may be a characteristic of species that exploit disturbed, spatially heterogeneous habitats through rapid multiplication of ramets connected by long, aerial runners or stolons.