Cytogenetics, biogeography and biology ofSantolina ageratifoliaBarnades ex Asso (Asteraceae: Anthemideae)

Abstract

Santolina ageratifolia Barnades ex Asso is a natural autohexaploid (2n = 6x = 54, 54 + 1B), endemic to Teruel Province, Spain and inhabits a substrate derived from sandstone, red limolite and quartzite. Three chromosome formulae are found: 30m + 12sm + 12st, present in 52% of the descendants (52 metaphase), 24m + 5m-1sm + 18sm + 6st in 39% of the descendants (39 metaphase) and 24m + 5m-1sm + 18sm + 6st + 1B in 9% of the descendants (9 metaphase). Chiasmata are mostly interstitial rather than terminal, giving rise to the formation of cruciform structures. The predominance of bivalent configurations in the meiosis and the exclusively bivalent formation in four individuals indicate that this species has a strong tendency towards diploidization. Secondary association of bivalents is observed in the number of 2, 4-6 chromosomes associated, the average being 4.21 ± 1.20 chromosomes. The variation in the chromosomal characteristics suggests chromosome translocation and/or inversions. This species is partially sterile, with a mean pollen fertility of 40.56% and a mean fructification of 34.24%. The frequencies of multivalents and pollen fertility have a strongly significant effect on fructification percentage. Phenotypic variation in habits is not correlated with karyotype characteristics. The cytogeography of the polyploid taxa of the Santolina rosmarinifolia aggregate is discussed.

Morphological Variation within and Between taxa of the Santolina rosmarinifolia L. (Asteraceae: Anthemideae) Aggregate

“…They show a less diverse ecological preference and are located on soils derived from limestone, marl, gypsiferous marl, and clay. The disjunctive distribution of the polyploids arose from fragmentation or contraction of the species range, preventing gene flow between them ( Richardson et al 2003 ) and allowing fixation of chromosomal, ontogenetic, and morphological changes, which favored differentiation and allopatric speciation ( Marlowe and Hufford 2007 ;Rivero-Guerra 2008c ). In addition, the results suggest that the variation between taxa is not associated with ploidy level because all taxa are significantly different from each other.…”

“…rosmarinifolia subsp. arrabidensis (tetraploid) [ Rivero-Guerra 2008c ]. Furthermore, the mean of the number of lobes of the middle leaves of the flowering and sterile stems is increased by polyploidy in S .…”

Morphological and cytotype variation of wild kiwifruit (Actinidia chinensis complex) along an altitudinal and longitudinal gradient in central-west China

“…Consequently, polyploids tend to exhibit distinct morphological characteristics and geographical distribution when compared with their parental diploids in heterogeneous climatic or environmental conditions (e.g. Richards, 1997; Levin, 2002; Mable, 2003; Rivero‐Guerra, 2008).…”

Cytogenetics, Geographical Distribution, Pollen Stainability and Fecundity of Santolina impressa (Asteraceae: Anthemideae)

“…This indicates that the crossing-over frequency within the inverted segment is high, and consequently the number of duplication-deficiency gametes is high. This explains the mean value of pollen stainability in the tetraploid cytotype of S. pectinata (Rivero-Guerra 2008a) and in S. ageratifolia (Rivero-Guerra 2008c). It also explains the lower percentage of fruiting of these two taxa (49.91% in the tetraploid cytotype of S. pectinata and 34.24% in S. ageratifolia) than in the other taxa of this aggregate.…”

“…This phenomenon also occurs in S. pectinata (Rivero-Guerra 2008a) and in S. ageratifolia (Rivero-Guerra 2008c). The presence/absence of sub-telocentric chromosomes suggests Robertsonian translocations.…”