Nothoscordum montveidense Sensu Lato: New Polyploid Cototypes from Argentina

Two natural cytotypes of the Nothoscordum montevidensecomplex are described for the southeastern region of Buenos Aires province, Argentina. The cytotypes are 2n = 6x = 24 and 2n = 8x = 32 with metacentric chromosomes (m). Cytological and morphological evidence indicates that these cytotypes belong to N. montevidense ssp. latitepalum, although this subspecies is 2n = 4x = 16m. The probable origin of these cytotypes is discussed.

The complex is distributed from Uruguay and Brazil to Argentina. In the latter country, N. montevidense s. 1. occurs in lowland fields, in meadows, and on roadsides. The specimens are characterized by yellow flowers in several-flowered inflorescences (exceptionally one-flowered) with single bulbs or with bulblets and rhizomes. The plants grow in full sunlight and flower in spring and fall.
The present paper deals with the description of polyploid populations belonging to the N. montevidense complex from the southeastern region of Buenos Aires province.

MATERIALS AND METHODS
Four populations of the N. montevidense complex from Balcarce (62 7, 637, 645, 728) and one from Mar Chiquita (639) were analyzed. Plants of each locality were maintained in clay pots. Voucher specimens were deposited in the herbaria at Balcarce (BAL) and Buenos Aires (SI). For the proper determination of the plant material, morphological measurements of a total of 40 individuals from the five natural populations were made. The provenance and karyotypes of the examined material are listed in Table 1.
We determined chromosome numbers from root tips using the technique of Nunez et al. (1974). Meiotic analyses were made by squashing anthers, which previously had been fixed in alcohol: acetic acid (3: 1), in acetic acid (45%) and staining them by following Snow's technique (Snow 1963). Drawings were prepared by the use of a Wild drawing apparatus and a Wild M-20 standard microscope. Chromosome types are indicated m and t in accordance with the nomenclature proposed by Levan, Fredga, and Sandberg (1964). Pollen fertility was estimated by using the technique proposed by Alexander (1969).

Cytological Analysis and Fertility
We found natural populations of the N. montevidense complex with a somatic complement of24 (cytotype I) (Fig. 1) and 32 m-chromosomes (cytotype II) (Fig.  2). On the basis of centromeric index (i), the m-chromosomes are metacentric and show a size gradation, with a mean index of 4 7 micrometers (i = short arm x I DO/ total chromosome length).
fhexavalent. Arrows indicate a chain trivalent and a chain quadrivalent.-4. Upper view ofa flower ofcytotype I. The inset shows a closed flower with a streak on the outer tepa!. (Fig. 1-2, scale = 10 /-tm ; Fig. 3, x 5000; Fig. 4, x 3.5 [inset, x 2]). In the genus Nothoscordum. meiosis occurs inside the bulb. This fact, as well as the one-flowered condition of these cytotypes, makes it difficult to analyze meiosis. For this reason, it has not been possible up to now to study meiosis in cytotype II. Chromosome pairing was analyzed at first metaphase in one clone of cytotype I (Fig. 3). The maximum pairing resulted in three hexavalents, one quadrivalent and one bivalent, and the minimum in twelve bivalents (Table 2). Because we observed a maximum pairing we consider that the chromosome complement is cytologically auto hexaploid.
Both cytotypes are morphologically similar and so are their chromosomes. On this basis, it is postulated that cytotype II would be an autooctoploid.
Pollen from several plants of both cytotypes averaged 90% stainability. Seed set in selfed plants (hand-pollinated) averaged 0-3 seeds per fruit, whereas outcrossed plants averaged 15-20 seeds per fruit. Preliminary crosses between plants of cytotype I and cytotype II were successful, yielding up to 20 viable seeds per fruit.

Habitat and Morphology
Four of the studied populations grow in lowlands fields on flooded heavy clay soils, and one (728) on a hill of the Balcarce region (Table 1). In population 637. both cytotypes grow sympatrically.
Octoploid populations, which have been found in two widely disjunct regions, consisted of plants that were not morphologically separable from hexaploids in the same areas. Both cytotypes had one-flowered inflorescences (occasionally twoflowered under cultivation) with bright yellow flowers. The outer tepals were ovate with a purple streak on the outer face below (Fig. 4).
Because of the short flowering period, the described cytotypes were hard to find in the field. Flowering occurs in full sun along with the flowering of Oxalis chrysantha Prog. The cytotypes flowered from mid to late October along with ssp. minarum, also a yellow-flowered subspecies, while a white-flowered species, N. bonariense (Pers.) Beauv., 2n = 22m + 4t (Nunez, Frayssinet, and Rodriguez 1972), reached full flowering approximately a week later when both cytotypes and ssp. minarum had already dispersed their seeds.
Although the cytotypes and ssp. minarum present an overlapping flowering period, we did not find natural hybrids between them, but did observe plants (2n = 27m + 2t) intermediate to the cytotypes and N. bonariense. We also found one specimen with 2n = 28m from population 637 morphologically and cyto- Both cytotypes reproduce successfully by sexual and asexual means. The individuals have vegetative propagation and are capable of developing clonal patches which reach variable sizes within the dominant populations of diploid ssp. minarum and N. bonariense. Morphological differences between both cytotypes and sympatric ssp. minarum are shown in Table 3.

Hypotheses on the Origin of the Cytotypes
Studying the inheritance ofB chromosomes, Luchini and Nicolini (pers. comm.) found two tetraploid and three triploid plants in the offspring of diploid ssp. minarum. The origin of the tetraploid cytotypes could be due to unreduced gametes in the diploid parents. Unreduced gametes with lO chromosomes, fertilized by normally reduced gametes, would provide the complement of 15 chromosomes observed in the triploid hybrids.
We have found no tetraploid plants with 2n = 16 in the study area. The discovery of this ploidy level would support the hypothesis about the origin of these cytotypes from 2n = 16m ancestors through sexual polyploidization. Also, we have found no diploids with 2n = 8m as reported by Crosa (1972). We conclude that cytotype I is auto hexaploid and cytotype II is autooctoploid, based on the existence of 2n = 8m and 2n = 16m in the N. montevidense complex.
The described cytotypes confirm that polyp10idization is an active mechanism in the evolution of the N. montevidense complex.