Stony endocarp dimension and shape variation in prunus section prunus

Abstract

Background and aims: Identification of Prunus groups at subspecies or variety level is complicated by the wide range of variation and morphological transitional states. Knowledge of the degree of variability within and between species is a sine qua non for taxonomists. Here, a detailed study of endocarp dimension and shape variation for taxa of Prunus section Prunus is presented.

Methods: The sample size necessary to obtain an estimation of the population mean with a precision of 5 % was determined by iteration. Two cases were considered: (1) the population represents an individual; and (2) the population represents a species. The intra-individual and intraspecific variation of Prunus endocarps was studied by analysing the coefficients of variance for dimension and shape parameters. Morphological variation among taxa was assessed using univariate statistics. The influence of the time of sampling and the level of hydration on endocarp dimensions and shape was examined by means of pairwise t-tests. In total, 14 endocarp characters were examined for five Eurasian plum taxa.

Key results: All linear measurements and index values showed a low or normal variability on the individual and species level. In contrast, the parameter 'Vertical Asymmetry' had high coefficients of variance for one or more of the taxa studied. Of all dimension and shape parameters studied, only 'Triangle' differed significantly between mature endocarps of P. insititia sampled with a time difference of 1 month. The level of hydration affected endocarp dimensions and shape significantly.

Conclusions: Index values and the parameters 'Perimeter', 'Area', 'Triangle', 'Ellipse', 'Circular' and 'Rectangular', based on sample sizes and coefficients of variance, were found to be most appropriate for further taxonomic analysis. However, use of one, single endocarp parameter is not satisfactory for discrimination between Eurasian plum taxa, mainly because of overlapping ranges. Before analysing dried endocarps, full hydration is recommended, as this restores the original dimensions and shape.

Fig. 1.

Overview of the basic linear endocarp measurements. Left: lateral view; right: ventral view.

Fig. 2.

Illustration of the linear measurements and index values, by means of minimum and maximum values of the reference samples. SL, ST, 100ST/SL: endocarps in lateral view; SW, 100SW/SL: endocarps in ventral view; 100ST/SW: endocarps in apical view; SL²/(ST × SW): endocarps in lateral view (left) and in apical view (right). Values for SL, SW, ST are expressed in mm. Abbreviations used are explained in Table 2.

Fig. 3.

Illustration of Brewer's parameters used in this study, by means of minimum and maximum values of the reference samples. For all endocarps the lateral view is displayed. Triangle = the ratio of the proximal end width to the distal end width, w₁/w₂; Ellipse and Circular: fitting precision R²; Rectangular = the ratio of the maximum area of the inscribing rectangle to the minimum area of an enclosing rectangle, S_in/S_out; Vasym = (Σ|m – m_i|)/number of rows, where m is the position of the vertical axis (determined by detecting the leftmost and rightmost points of the endocarp and dividing it in half to find the centre), m_i is the midpoint of the row L_i. Values for Perimeter and Area are expressed in mm. Abbreviations used are explained in Table 2.

Fig. 4.

Overview of the minimum, mean and maximum values with the corresponding endocarp images (lateral view) for each taxon and for all parameters used in this study. For SW and derived parameters, the minimum, mean and maximum values are shown without the corresponding endocarp images. Values for SL, SW, ST, Perimeter and Area are expressed in mm. Abbreviations used are explained in Table 2.

Fig. 5.

Mean values of Perimeter for endocarps of three different individuals belonging to three different taxa (P. domestica, P. cerasifera, P. spinosa) exposed to different hydration conditions. For full explanation of treatments, see Materials and Methods.