Flow cytometric, chromosomal and morphometric analyses challenge current taxonomic concepts in the Portulaca oleracea complex (Portulacaeae, Caryophyllales)
Portulaca oleracea is a noxious annual weed of worldwide distribution in temperate to tropical climates. Its taxonomy has been treated in contradictory ways in the past. Various microspecies have been described, lumped into a single species by other authors. We re‐examined the importance of seed siz...
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| Published in | Botanical journal of the Linnean Society Vol. 179; no. 1; pp. 144 - 156 |
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| Main Authors | , , |
| Format | Journal Article |
| Language | English |
| Published |
Oxford
Blackwell Publishing Ltd
01.09.2015
Oxford University Press |
| Subjects | |
| Online Access | Get full text |
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| Summary: | Portulaca oleracea is a noxious annual weed of worldwide distribution in temperate to tropical climates. Its taxonomy has been treated in contradictory ways in the past. Various microspecies have been described, lumped into a single species by other authors. We re‐examined the importance of seed size and ploidy variation, previously applied as the most important taxonomic characters, for systematic classification based on accessions from Europe, Asia, Africa and South America using flow cytometry, chromosome counting and morphometry. Sixteen microspecies and six transitional forms, covering the ploidy and seed character variation, proposed for the complex, were studied from 178 populations. Portulaca grandiflora was included as a reference species from outside the complex. DNA hyper‐pentaploidy or hexaploidy were inferred for the majority of accessions which exhibited the full range of seed size. It is recommended that the only species of lower ploidy (either diploid based on x = 12 or tetraploid based on x = 12) encountered, P. nicaraguensis, should be separated from the P. oleracea complex as it deviates in base chromosome number and monoploid genome size. The frequency distribution of seed size was continuous and unimodal within the wild taxa of the complex and in pairs of taxa defined by testa sculpture. Seed size of DNA hexaploids was slightly negatively correlated with sample/standard fluorescence intensities. Our results conflict with the current microspecies concept. Possible reasons underlying the discrepancy are discussed and strategies for future systematic research are suggested. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 179, 144–156. |
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| Bibliography: | Supporting Information S1. Testa sculpture types in the Portulaca oleracea complex: the morphologically diagnostic area is restricted to the central part of the upper and lower sides of seeds. The peripheral zone of the seed is of little relevance. Types are defined by the combination of the following elements: stellate (star-shaped) cells, isodiametric or elongated, smooth or with papillae and/or tubercles, the central part flat or convex, the rays short or elongated, clearly visible or covered with papillae; tubercles are large protuberances (0.03 mm diameter), papillae are smaller (0.01-0.02 mm diameter). Supporting Information S2. Accession number (acc.), taxonomic assignment (according to Danin et al., 1979, 2008; Danin, 2000, 2011; Danin & Raus, 2012), geographical origin, collection history, and depository of vouchers of 178 Portulaca accessions studied. Supporting Information S3. Mean sample/standard DAPI fluorescence ratios ('index mean') of 159 accession of the Portulaca oleracea complex representing 21 taxa (including six transitional forms) and three accessions of P. grandiflora (in total 162 accessions and 22 taxa). 'N measurements' is the number of flow cytometrically analysed samples. One to five seedlings were measured per sample. Supporting Information S4. Variation of seed length in wild species of the Portulaca oleracea complex. The statistics are based on the means for accessions usually analysed for 20 seeds. Accessions are grouped by the type of testa sculpture (Supporting Information S2). Accessions with intermediate testa types were excluded. Supporting Information S5. Published chromosome numbers for taxa of the Portulaca oleracea complex not included in the present study or not determined on the level of microspecies ('P. oleracea s.l.'). ark:/67375/WNG-SMCXQL3D-4 ArticleID:BOJ12309 istex:5801E25E41A06635F1047CEA3F1A13F4443A0364 ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
| ISSN: | 0024-4074 1095-8339 |
| DOI: | 10.1111/boj.12309 |