abstract

The architectural model of Spartium junceum L. The architectural model of Spartium junceum L. was studied stressing its diversity in plants of different physiological age. The first part of the study describes the phyllotaxis and the different types of shoots that are produced by the broom plants. The second part discusses the bud growth (vegetative or reproductive) in relation to the type of shoot and to the position along the axis, and finally the bud break organization. In the third part, the elongation rate and the total growth of the shoots are related to the architectural model, the physiological age, and the adaptive value. The leaves are opposite in all types of shoots or plant ages, being distances between leaves in a pair much smaller than that between pairs. Each successive pair of opposite leaves is arranged at a right angle to the previous pair. The distance between pairs of leaves is higher in the middle part of the shoot, so as inside the pair. Young individuals elongate more the primary shoots, producing a higher amount of sylleptic shoots, than older plants, while the latter have a higher percentage of bud break. Too many shoots in expanding young plants, each of which would be singly disadvantaged, could lead to a dilution of resources. Such a behavior can give to young broom plants architecture an adaptive value to compete with herbs in the early stages of the colonization of abandoned fields. Under these conditions, broom plants assume a soaring shape with an ovoid canopy. On the contrary, in senescent or adult individuals the proliferation of short shoots is favored in comparison with sylleptic growth and shoot elongation (low and uniform). Therefore, during the maturity the plant tends to assume an expanded shape with an external crown of short reproductive branches and an internal cavity whose dimensions increase with years.

keywords

adaptive value, broom, bud break, phyllotaxis, plant canopy, sylleptic shoots