Chromosome diversity of South American Oxalis (Oxalidaceae)

Mitotic or meiotic chromosome studies are reported for 39 species or subspecies of Oxalis from South America belonging to 14 sections. Chromosome numbers of 34 of these taxa are reported for the first time. Diploids and polyploids with six different basic chromosome numbers x=5, 6, 7, 8, 9 and 11 are described. Thirteen species of subgenus lhamnoxys were analysed and two new basic chromosome numbers were observed in diploid entities of this subgenus, x = 6 and x=9. The underground stem-bearing entities of Oxalis subgenus Oxalis studied (in sections Articulatae, Jonoxalis and Palmatifoliae) are mostly diploids and polyploids with a basic chromosome number x=7. Five species of section Carnosa are diploids with x = 9. In species of sections Rosea, Ortgieseae, Clematodes and Laxae the basic chromosome numbers x = 6, 7, 8 and 9 were observed. Groups of related species sharing the same chromosome number are discussed with the aim of improving the infrageneric delimitation of the genus. The basic chromosome number x=6 seems to be primitive in the genus and other basic chromosome numbers probably appeared several times in the course of chromosome evolution of Oxalis .     

中国酢浆草属一新种

珠芽酢浆草　新种　图 1ＯｘａｌｉｓｂｕｌｂｉｌｌｉｆｅｒａＸ .Ｓ .ＳｈｅｎｅｔＨ .Ｓｕｎ ,ｓｐ .ｎｏｖ .ＴＹＰＥ :Ａｎｈｕｉ (安徽 ) ,Ｊｉｎｚｈａｉ (金寨 ) ,ｉｎｔｈｅＴｉａｎｔａｎｇｚｈａｉ(天堂寨 ) ,ａｌｔ.15 0 0ｍ ,2 0 0 0 - 10 - 2 1,ＳｈｅｎＸｉａｎ ｓｈｅｎｇ 2 0 0 88,(ｈｏｌｏｔｙｐｅ ,ＫＵＮ ,ｈｅｒｅｄｅｓｉｇｎａｔｅｄ) .Ｆｉｇ .1.ＡｆｆｉｎｉｓＯｘａｌｉｓａｃｅｔｏｓｅｌｌａｅＬ .,ｓｅｄｐｌａｎｔｉｓ2 - 5ｃｍａｌｔｉｓ .,ｓｔｏｌｏｎｉｆｅｒｉｓ,ｆｏｌｉｏｌｉｓｐｅｔｉｏｌｕｌａｔ…     

Genetic basis of tristyly in tetraploid Oxalis alpina (Oxalidaceae)

The inheritance of style‐morphs was investigated in tetraploid populations of tristylous Oxalis alpina (Oxalidaceae) to determine if alleles controlling style‐morphs are expressed at duplicated loci. In tetraploid populations, a dominant S allele leads to expression of the short‐styled phenotype at the short/non‐short locus and is epistatic to the M allele at the mid/long locus. The M allele results in expression of the mid‐styled phenotype but only if the S allele is absent. Long‐styled morphs are homozygous recessive at the short and mid loci. Test crosses of many tetraploid short‐styled individuals resulted in segregations of short‐, mid‐ and long‐styled individuals which, because of linkage between the short and mid loci, can only occur with polyploidy and expression of alleles at duplicated loci. Segregation patterns from three crosses suggest the possibility of disomic inheritance via preferential pairing of chromosomes in tetraploid populations of O. alpina. Segregation patterns in the progeny of mid‐styled individuals indicated that only a few individuals had more than one copy of the M allele, despite the potential for accumulation of M alleles via self‐fertilization of partially self‐compatible mid‐styled morphs in some populations. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 179 , 308–318.     

Population variation of leaflet sleep movements in Oxalis grandis (Oxalidaceae)

To identify intraspecific variation in the expression of circadian leaflet movements, we observed changes in leaflet elevation angle in a controlled environment and in the field. Two morphologically and ecologically distinct populations of Oxalis grandis were compared: a typical mesic forest ecotype and an atypical, densely hirsute ecotype found on partially exposed shale outcroppings. Significant genotypic variation was detected within both populations. The controlled environment experiment revealed significant differences in the intrinsic rhythm between the two populations, primarily at the beginning and end of the photophase. We observed leaflet ascent and descent prior to lights-on and lights-off, respectively, processes we define as anticipatory. Hirsute ecotype plants showed a greater anticipation of lights-on, whereas the mesic ecotype plants showed a greater anticipation of lights-off. In the field, significant differences in leaflet elevation between the populations occurred in early morning and late afternoon, but not immediately preceding dusk. Contrary to the controlled environment experiment, mesic ecotype plants showed greater anticipation of dawn; plants from both populations showed similar anticipation of dusk. Plants of the hirsute ecotype exhibited higher sensitivity to sudden fluctuations in light level. We hypothesize that differences in light sensitivity partially explain the differences in the leaflet angle patterns between the field and controlled environments.     

Flower-visiting bees and the breakdown of the tristylous breeding system of Eichhornia azurea (Swartz) Kunth (Pontederiaceae)

Populations of Eichhornia azurea (Swartz) Kunth (Pontederiaceae) are often composed of three floral morphs that differ in style length and anther position. Hence, E. azurea is described as tristylous. For sexual reproduction the plant requires specialized pollinators able to transfer pollen from flowers with long-, mid-, or short-level anthers to flowers with long-, mid-, or short-styles, respectively. This is because within a floral morph, self-incompatibility is the rule. Populations of E. azurea were studied from six localities in south-eastern Brazil (São Paulo and Minas Gerais). The frequencies of floral morphs, floral morphology and flower-visiting bees were recorded in each population. Ten different bee species were observed visiting plants. Four of them were considered generalist bees and not appropriate for legitimate pollination of the three floral morphs. Another three species were considered opportunists and only three species were considered to be potential pollinators. At the coastal region (Juréia), the plant population lacked the short-styled morph and the mid-styled morph and exhibited a semi-homostylous condition, in which the low-level anthers were adjacent to the stigma. This morph showed high level of self-compatibility. The disappearance of the short-styled morph from this region is likely correlated with the absence of Ancyloscelis gigas Friese, a specialized long-tongued bee that is oligolectic on this plant in other localities.  © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 77 , 499–507.     

Three new species and a revised key to species of Oxalis section Polymorphae (Oxalidaceae)

Three new species of Oxalis sect. Polymorphae are here described and illustrated: Oxalis artemioides, O. calcicola, and O. monochasiata. These species have narrow geographic distributions, each being known from just one location. Oxalis artemioides differs from other species of the section by the glabrous stem, narrow terminal leaflets (8–10.5 × 2 mm), and inflorescences with elongated dichasial branches bearing flowers only in the distal portion. Oxalis calcicola differs from other species by having the young stem with adpressed-retrorse trichomes, inflorescences shorter than adjacent leaves, short dichasial branches (0.5–3 mm long) with flowers densely grouped along the entire length, and glabrous pedicels. Oxalis monochasiata is remarkable because of its monochasial inflorescence and the two-ovulate carpels, both features unique within Oxalis sect. Polymorphae. The new species are compared to similar species of the section, and information on distribution and habitat, phenology, and conservation status according with IUCN criteria are provided. Geographic distribution maps, lists of examined materials and an identification key for species of this section are also presented.     

A new species of Oxalis section Corniculatae (Oxalidaceae) from the Balearic islands

A new species, Oxalis ferae Llorens, Gil & Cardona (Oxalidaceae) from the Balearic islands (Spain) is described and illustrated. It is considered to be endemic to Mallorca. The morphological differences between the more closely related taxa of Oxalis section Corniculatae are discussed. IUCN threatened category and observations on the ecology of the populations are noted.  © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 148 , 489–493.     

Purging of inbreeding depression within a population of Oxalis alpina (Oxalidaceae)

? Premise of the study: Variation among individuals in levels of inbreeding depression associated with selfing levels could influence mating system evolution by purging deleterious alleles, but empirical evidence for this association is limited. ? Methods: We investigated the association of family-level inbreeding depression and presumed inbreeding history in a tristylous population of Oxalis alpina (Oxalidaceae). ? Key results: Mid-styled individuals possessed the greatest degree of self-compatibility (SC) and produced more autogamous capsules than short- or long-styled individuals. Offspring of highly self-compatible mid-styled individuals showed reduced inbreeding depression. Mid-styled plants that produced capsules autogamously exhibited reduced stigma-anther separation compared to mid-styled plants that produced no capsules autogamously. Reduced inbreeding depression was not correlated with stigma-anther separation, suggesting that self-compatibility and autogamy evolve before morphological changes in stigma-anther separation. ? Conclusions: Purging of inbreeding depression occurred in SC mid-styled maternal families. Low inbreeding depression in SC mid-styled plants may lead to retention of the mid-styled morph in populations, despite the occurrence of higher selfing rates in mid-styled relative to short- or long-styled morphs. Variation among individuals in levels of self-fertilization within populations may lead to associations between inbreeding lineages and lower levels of inbreeding depression, influencing the evolution of mating systems.     

Origins of domestication and polyploidy in oca (Oxalis tuberosa : Oxalidaceae): nrDNA ITS data

As part of a study aimed at elucidating the origins of the octoploid tuber crop "oca," Oxalis tuberosa, DNA sequences of the internal trancribed spacer of nuclear ribosomal DNA (nrDNA ITS) were determined for oca and several wild Oxalis species, mostly from Bolivia. Phylogenetic analysis of these data supports a group of these species as being close relatives of oca, in agreement with morphology and cytology, but at odds with traditional infrageneric taxonomy. Variation in ITS sequences within this group is quite low (0-7 substitutions in the entire ITS region), contrasting with the highly divergent (unalignable in some cases) sequences within the genus overall. Some groups of morphologically differentiated species were found to have identical sequences, notably a group that includes oca, wild populations of Oxalis that bear small tubers, and several other clearly distinct species. The presence of a second, minor sequence type in at least some oca accessions suggests a possible contribution from a second genome donor, also from within this same species group. ITS data lack sufficient variation to elucidate the origins of oca precisely, but have identified a pool of candidate species and so can be used as a tool to screen yet unsampled species for possible progenitors.     

Pollen and stigma size changes during the transition from tristyly to distyly in Oxalis alpina (Oxalidaceae)

• Pollen and stigma size have the potential to influence male fitness of hermaphroditic plants, particularly in species presenting floral polymorphisms characterised by marked differences in these traits among floral morphs. In this study, we take advantage of the evolutionary transition from tristyly to distyly experienced by Oxalis alpina (Oxalidaceae), and examined whether modifications in the ancillary traits (pollen and stigma size) respond to allometric changes in other floral traits. Also, we tested whether these modifications are in accordance with what would be expected under the hypothesis that novel competitive scenarios (as in distylous‐derived reproductive system) exert morph‐ and whorl‐specific selective pressures to match the available stigmas.
• We measure pollen and stigma size in five populations of O. alpina representing the tristyly–distyly transition.
• A general reduction in pollen and stigma size occurred along the tristyly–distyly transition, and pollen size from the two anther levels within each morph converged to a similar size that was characterised by whorl‐specific changes (increases or decreases) in pollen size of different anthers in each floral type.
• Overall, results from this study show that the evolution of distyly in this species is characterised not only by changes in sexual organ position and flower size, but also by morph‐specific changes in pollen and stigma size. This evidence supports the importance of selection on pollen and stigma size, which increase fitness of remaining morphs following the evolution of distyly, and raises questions to explore on the functional value of pollen size in heterostylous systems under pollen competition.

     

The spatio-ecological segregation of different cytotypes of Oxalis obtusa (Oxalidaceae) in contact zones

Contact zones of different cytotypes provide an opportunity to address evolutionary mechanisms underlying the origin, establishment and maintenance of karyological diversity at intraspecific level. We explored the fine-scale distribution of ploidy levels of Oxalis obtusa in seven mixed-ploidy sites in the Western and Northern Cape Provinces, South Africa, and searched for potential isolating barriers promoting assortative mating. Five different ploidy levels (2x, 3x, 4x, 6x and 8x) were detected among 336 samples collected at 112 microsites. The studied sites were inhabited by two (2 sites), three (4 sites) or even all five (1 site) different cytotypes. Despite their sympatric growth, different ploidies show some spatio-ecological segregation. The greatest differences among microsites hosting different cytotypes were found in precipitation parameters. There is a clear altitudinal gradient in ploidy composition in the most ploidy-variable site, Pakhuis Pass. Our results show that a combination of niche partitioning and clumping of same-ploidy individuals due to vegetative reproduction seems to be efficient reproductive barriers, which limit inter-ploidy gene flow in the zones of ploidy contact and contribute to the long-term maintenance of cytotype mixtures in O. obtusa.     

入侵植物酢浆草在中国的花型分布特点及自花授粉

通过野外调查和馆藏标本(IBSC)的查阅,对广泛分布于中国的入侵植物酢浆草Oxalis corniculata的花型、开花物候、访花昆虫和花粉胚珠比(P/O)进行了观测.通过人工辅助授粉实验检测了其繁育系统;使用扫描电子显微镜(SEM)观察了自花花粉在柱头上的萌发情况并使用荧光显微镜(FM)观察了花粉管在花柱中的生长情况.结果表明:酢浆草在中国有3种花型,半等长花柱型、准等长花柱型和长花柱型,大部分的居群只有半等长花柱型,分布于人为干扰较大的生境(如路边);云南安宁松树林下的自然居群和采自广东的两份标本为长花柱型花:少部分居群内兼有半等长花柱型和准等长花柱型植株.酢浆草花期从2月到11月.其中3_9月为开花高峰期:单花花期2天,花开当天傍晚花瓣会合拢,第二天早上花瓣再次打开,到花开第二天傍晚花瓣萎蔫.花蕾开放前花药已开裂,柱头有活性,大部分花粉散落到柱头上,且花粉已开始萌发;花粉胚珠比为83.3±33.08.有少量花蜜分泌.唯一的访花昆虫为一种小灰蝶Pseudozizeeria sp.,但并不是有效的传粉者.开花前套袋处理结实率(88.12±3.38)与自然结实率(88.03±2.48)基本没有差异:荧光显微镜观察证明自花花粉的花粉管可在花开第一天生长到达胚珠,说明酢浆草半等长花柱植株是自花授粉.     

Leaf longevity of Oxalis acetosella (Oxalidaceae) in the Catskill Mountains, New York, USA

Leaf habit correlates with multiple physiological traits. Understanding ecophysiology is therefore dependent on knowledge of leaf habit. A variety of leaf habits exists within forest understory plant communities. Oxalis acetosella is one such understory plant and has long been considered a wintergreen, meaning that it keeps a set of leaves for one full year, replacing them with a new set during spring. To assess the leaf habit of O. acetosella and place it into a classification scheme of leaf habits, leaves of four populations of O. acetosella were repeatedly censused for two years in a northern hardwood forest of the Catskill Mountains, New York, USA. New leaves developed and old leaves senesced throughout the year, yielding a continual replacement of leaves and a summer peak in leaf number. Leaves that developed in the fall and winter had longer maximum life spans than leaves that developed during the summer. The name "seasonalgreen" is suggested to describe the continual development, senescence, and presence of leaves and annual peak in leaf number within O. acetosella. The functional significance of this leaf habit in this species and the possibility of its presence in other species deserve further study.     

Expression of stylar incompatibility in the Andean clonal tuber crop oca (Oxalis tuberosa Mol., Oxalidaceae)

Long-, mid-, and short-styled clonal accessions of oca (Oxalis tuberosa) were intercrossed in a complete diallelic design. Pollen tube growth in styles was monitored in all diallelic crosses. Pollen fertility was estimated by two tests: staining of pollen grains with aceto-carmine and detection of β-galactosidase activity by the substrate X-Gal. The two methods of pollen fertility estimation were equally useful to detect fertility levels. Pollen originating from short stamens had the highest fertility (85%) and pollen from long stamens had the lowest fertility (70%). Pollen fertility was high throughout, but its degree varied with the stylar morph on which the pollen was formed. Long-styled accessions had the highest rates of fertile pollen. Differences in pollen fertility at different anther levels in the same style morph were also apparent. Pollen grain diameter of the six morph-anther level combinations was inversely correlated with pollen fertility. Pollen grains from long stamens were the largest and pollen grains from short stamens were the smallest. Neither pollen fertility nor pollen grain size had an influence on pollen tube growth in the style or on fruit and seed set. Pollen tubes growing within the styles were inhibited at a different level for each of the 18 cross combinations in the diallel. Although legitimate crosses had greatest pollen tube growth, some of the illegitimate inter- and intramorph crosses had equally high scores. Of all illegitimate crosses, mid-styled seed parents had the lowest level of stylar incompatibility. Fruit and seed set were highly correlated with the extent of pollen tube growth in the style. The number of pollen tubes entering ovules in a flower was in good agreement with the number of seeds produced per fruit. Therefore, it is concluded that stylar incompatibility is the major determinant of limited seed formation in oca even in the most successful legitimate cross combinations. Received: 1 September 1999 / Revision accepted: 4 April 2000     

Fecundity and fitness in cross-compatible pollinations of tristylous North American Lythrum salicaria populations

As heterostyly and self incompatibility are linked in tristylous L. salicaria, all cross-compatible pollinations – those between anthers and styles of the same level – should produce viable seed. The rigor of this theory was tested using seed set and germination of cross-compatible pollinations in 18 naturalized L. salicaria populations in Minnesota/Wisconsin (n=342 genotypes; n=86 shorts, n=127 mids, and n=129 longs). Seed set for short-styled genotypes ranged from zero to 135 (36+38); mids–0–156, (53+39), and longs–0–151 (59+39). Mean seed set per capsule was not significantly different for mids and longs, but both were significantly greater than that of shorts (F=14, P<0.0001). Zero seed set frequently occurred in most compatible crosses, in contrast with theoretical expectations. The high percentage of populations deviating from normality must be due to incompatibility. An incompatibility system independent of heterostyly could cause this, where failed crosses result from matches of incompatibility specificities in pollen and pistil. This independence is questionable, however, given the non-significant difference in failed outcrosses for pooled χ² comparing within and between populations (χ²=0.395, P>0.5). A sporophytic incompatibility model is proposed with a minimum of three specificities. Zero seed set in compatible crosses is due to the addition of alleles from L. alatum, a distylous species that forms introgressive hybrids with L. salicaria. Reduced fecundity could increase the deficiency of shorts, and significantly greater seed germination of shorts could explain the continued presence of short-styled individuals in L. salicaria populations. Received: 3 February 2000 / Accepted: 25 March 2000