Guillermo A. Norrmann

Evolutionary implications of meiotic chromosome behavior, reproductive biology, and hybridization in 6x and 9x cytotypes of Andropogon gerardii (Poaceae).

Andropogon gerardii, big bluestem, has 60 and 90 chromosome cytotypes. Meiosis in the hexaploid was shown to be regular, although some secondary associations of bivalents form. Meiosis in the enneaploid (2n = 9z = 90) is irregular, leading to most gametes having unbalanced chromosome complements. Both cytotypes show considerable self-incompatibility. Cytotypes crossed freely, forming a variety of fertile euploids and aneuploids. Indistinguishable exomorphology, intermixing in natural populations, and compatibility suggest that A. gerardii is best understood as a cytotypically complex single species.

INTERSPECIFIC HYBRIDS BETWEEN FIVE PASPALUM SPECIES

Interspecific crosses were made among Paspalum intermedium Munro, P. haumanii Parodi, P. brunneum Mez, P quadrifarium Lam., and P. rufum Nees, species with both sexual diploid (2n = 20) and apomictic tetraploid cytotypes. Eight different interspecific hybrid progenies involving diploid species were recovered from crosses using P. intermedium or P. haumanii as the female parent. When P. rufum was the female parent in crosses with the other four species, only the hybrid with P. intermedium as pollen donor was recovered. Paspalum brunneum as female parent gave hybrid progenies only with P. rufum. All hybrids had 2n = 20 chromosomes, and the degree of meiotic pairing was high in most of them. Excepting P. haumanii x P. brunneum, all other hybrids had some pollen mother cells (PMC) with 10 II. Paspalum haumanii x P. brunneum had the least number of bivalents (mean = 4.7, maximum = 7 II). Almost complete pairing was observed in P. intermedium x P. haumanii and P. quadrifarium x P. brunneum, with a mean of 9.86 and 9.9 bivalents/PMC, respectively. The high degree of meiotic pairing in the hybrids is consistent with morphological and ecological affinities of the species as well as their geographical distribution. The data indicate that the genome of each of these species evolved from an ancestral common basic genome, and each of them may be a particular form of the I genome previously assigned to P intermedium. The low rate of crossability among these five species and the high sterility of the hybrids are important barriers preventing introgression.

Cytology and Reproductive Behavior of Paspalum equitans, P. ionanthum, and Their Hybrids with Diploid and Tetraploid Cytotypes of P. cromyorrhizon

Paspalum equitans is a sexual, cross-pollinated diploid (2n = 2x = 20) with normal meiosis. It has some potential for apomixis because one or two aposporous embryo sacs were observed beside the meiotic sac in 18.2% of the ovules. Regular meiotic behavior was confirmed in tetraploid (2n = 4x = 40) P. ionanthum (= P. guaraniticum), which has 20II at meiosis and is cross-pollinated. Hybrids were produced between P. equitans and diploid P. cromyorrhizon, a species with the basic N genome. A high degree of meiotic chromosome pairing in the hybrids demonstrated that P. equitans also has the N genome. However, these species are isolated because the F1 hybrids are sterile. Meiotic chromosome pairing in hybrids of P. ionanthum x diploid and tetraploid P. cromyorrhizon indicated that at least one genome of P. ionanthum is a form of the N genome. Moreover, 1-7III were observed in ca. 75% of pollen mother cells of P. ionanthum x diploid P. cromyorrhizon triploid hybrids, and quadrivalents were observed in P. ionanthum x tetraploid P. cromyorrhizon hybrids, which indicated that P. ionanthum contributed two homoeologous genomes. In the diploid P. cromyorrhizon x P. ionanthum cross, a tetraploid hybrid was recovered, indicating that an unreduced diploid gamete of P. cromyorrhizon was involved in the origin of this hybrid.

Chromosome number in South American species of Bothriochloa (Poaceae: Andropogoneae) and evolutionary history of the genus

Mitotic chromosome number of 14 taxa of Bothriochloa native to Argentina, Brazil and Uruguay were surveyed. Chromosome numbers of B. eurylemma, B. meridionalis and B. velutina are reported for the first time, with 2n = 6x = 60, and this ploidy level is the most common among the studied taxa. In addition, new cytotypes were found for B. alta (2n = 60), B. barbinodis (2n = 60), B. exaristata (2n = 80), B. laguroides var. torreyana (2n = 80), B. longipaniculata (2n = 60 and 80), B. perforata (2n = 60) and B. springfieldii (2n = 60). These numbers differ from those reported in the literature.

Taxon Delimitation in the Andropogon lateralis Complex (Poaceae) in Southern South America based on Morphometrical Analyses

Abstract In the tribe Andropogoneae, morphological variation is remarkable, mainly in the inflorescence on the pair of spikelets which are the core elements of the inflorescence. The genus Andropogon includes the Andropogon lateralis complex, which is distributed primarily in South and Central America, comprising approximately twelve taxa and inter-specific hybrids. The aim of this study was to assess morphological variation in the A. lateralis complex through morphometric analyses of specimens from natural populations. For this purpose, univariate ANOVA, as well as principal component analysis and discriminant analysis of 19 morphological variables of synflorescences were performed, revealing differences between species and interspecific hybrids. The selected diagnostic traits of species and hybrids based on quantitative characters of the synflorescences provided a valuable tool for taxonomic studies in the genus. The results obtained made it possible to generate the first identification key that includes both species and hybrids of the A. lateralis complex for South America.

ANDROPOGON × PARAGUARIENSIS, A NEW NAME FOR ANDROPOGON × VELUTINUS (POACEAE, ANDROPOGONEAE)

The new name Andropogon × paraguariensis Norrmann & Nagahama is proposed to replace the illegitimate name Andropogon × velutinus Norrmann & Nagahama, a natural hybrid from southern South America.

NOMBRES VÁLIDOS PARA HÍBRIDOS DEL COMPLEJO ANDROPOGON LATERALIS (POACEAE, ANDROPOGONEAE) SOBRE LA BASE DE ANÁLISIS MULTIVARIADOS

The Andropogon lateralis complex is constituted by 13 taxonomic entities: seven species and six class inter-specific hybrids distributed in Central and South America. Natural hybrids within this group are quite common due to lack of inter-specific barriers. These hybrids have been collected in the last two centuries and, in most cases, have caught the attention of taxonomists, who formally described several as new taxa. Therefore, taxonomic entities based on them have been validly published. In southern South America, among the ten taxonomic entities in the A. lateralis complex, five are natural hybrids and at least three possess legitimate names ( A. × coloratus , A. × lindmanii , and A. × subtilior ). Based on morphometric analyses and previous studies we propose that other two natural hybrids deserve taxonomic names. These entities are Andropogon × velutinus ( A . bicornis × A . glaziovii , = Andropogon sp 1 according to Zanin, 2001) and Andropogon × catarinensis ( A . bicornis × A . arenarius ). Taxonomic treatments of A . × velutinus and A . × catarinensis are presented.