Cytotaxonomy of the apocynaceae

Abstract

At present there is karyological information on ca 10% of the species and ca 30% of the genera of the Apocynaceae. Basic numbers of x = 6, 8, 9, I 0, 11, 12, 16, 18, 20, 21 and 23 have been assessed. Of these x = 11 is primitive, occurring in ca 60% of the genera.Those ofx = 6, 8, 9 and 10 have evolved by reduction, and x = 12 by increase from x = 1 I. In the subtribe Secondatiinae however, x = 12 is most likely the result of doubling x = 6. The numbers x = 16, 18 and 20 are likewise doubles of x = 8, 9 and 10 respectively. Those of x = 21, 23, and in one case, x = 20 are probably aneuploid products of doubles of x = 11.The two larger subfamilies, Plumerioideae and Apocynoideae have the basic numbers.x = 8, 9, 10 and 11 in common and are not separable on the basis of chromosomal evidence. The third small subfamily Cerberoideae is more homogeneous according to basic number, i.e. x = 10 and 20. Most genera are characterized by a constant basic number, but some have two basic numbers; these clearly are cases of infrageneric aneuploidy.Based on records in the literature two closely related genera Apocynum and Trachomitum appear to be characterized by a basic number of x = 8 as well as x = 1 i. This conflicting situation should be clarified by further karyological research. From the level of subtribe onwards some taxa have one basic number, but others are characterized by two or more numbers. The occurrence of similar basic numbers in different phylads of the family is considered to be the result of similar chromosomal evolution mechanisms.Approximately 22% of the investigated species are polyploid. Intrageneric polyploidy occurs with a frequency of about 12.5% and infraspecific polyploidy with less than 4%.The karyotypes observed are symmetrical: the chromosomes within a karyotype are similar in length with primary constrictions usually in a median position. In the Tabernaemontaneae however, it was observed that the karyotypes comprise one pair of distinctly heterobrachial chromosomes in addition to the metacentric ones. This tribe is also characterized by chromosomes which are relatively long.Most genera of the African continent, which are well known regarding their chromosome number, are characterized by x = ! 1. Exceptions are Strophantus (x = 9) with a mainly tropical African distribution. Two other genera with derived numbers, i.e. Gonioma with x = I 0 and Pachypodium with x = 9, occur in southern Africa and Madagascar. The genera with a non-African distribution are less known for their chromosome number. However, the available evidence suggests that evolution of derived numbers has occurred more frequently outside Africa than on this continent.

Is there a relationship between polyploidy and stressful environments? A case study of inselbergs in northeastern Brazil

“…This species is exclusive to inselbergs and rocky field vegetation in northeastern Brazil (Watanabe et al, 2009). Chromosomal counts of 2n = 20 have been reported for other genera of Apocynaceae, such as Strophanthus and Trachelospermum, as well as 2n = 18 for Allamanda, Pachypodium, and Prestonia (Van der Laan and Arends, 1985). Counts of 2n = 20 and 22 in the 2 species examined here is within the modal range (or near the mode number) for the family, and apparently they are diploids.…”

“…The family Apocynaceae (including the Asclepiadaceae sensu APG III, 2009) is a karyologically stable group, with 2n = 22 in a large majority of the species or polyploids with 2n = 44 and 66 (Van der Laan and Arends, 1985). The present count of 2n = 20 for Maxillaria tenuifolia is the first for the genus.…”

Citogenética de Angiospermas coletadas em Pernambuco: V

“…I) . Registro anterior de 2n= 16 para N. oleander foi considerado incorreto por Van der Laan & Arends ( 1985).…”

Karyomorphological Analysis of Different Varieties of <i>Tabernaemontana coronaria</i>

“…The chromosome complement of this species has been found to be homogeneous with 2n=22 and n=11 (Roy Tapadar and Sen 1960, Roy Tapadar 1964, Dutta and Maity 1972 except one report by Van der Laan and Arends (1985), where they found 2n=33 chromosomes. The different species of this genus contain 2n=22 chromosomes revealing basic number to be x=11 (Van der Laan and Arends 1985).…”

“…The different species of this genus contain 2n=22 chromosomes revealing basic number to be x=11 (Van der Laan and Arends 1985). Chromosome analysis of T. coronaria was carried out earlier which involved meiotic behavior in pollen mother cells (Raghuvanshi and Chauhan 1969, 1970, Chauhan and Raghuvanshi 1976.…”