Abstract
We have generated matK, rbcL, and nrITS2 DNA barcodes for 320 specimens representing all 18 extant genera of the conifer family Podocarpaceae. The sample includes 145 of the 198 recognized species. Comparative analyses of sequence quality and species discrimination were conducted on the 159 individuals from which all three markers were recovered (representing 15 genera and 97 species). The vast majority of sequences were of high quality (B 30 = 0.596–0.989). Even the lowest quality sequences exceeded the minimum requirements of the BARCODE data standard. In the few instances that low quality sequences were generated, the responsible mechanism could not be discerned. There were no statistically significant differences in the discriminatory power of markers or marker combinations (p = 0.05). The discriminatory power of the barcode markers individually and in combination is low (56.7% of species at maximum). In some instances, species discrimination failed in spite of ostensibly useful variation being present (genotypes were shared among species), but in many cases there was simply an absence of sequence variation. Barcode gaps (maximum intraspecific p–distance > minimum interspecific p–distance) were observed in 50.5% of species when all three markers were considered simultaneously. The presence of a barcode gap was not predictive of discrimination success (p = 0.02) and there was no statistically significant difference in the frequency of barcode gaps among markers (p = 0.05). In addition, there was no correlation between number of individuals sampled per species and the presence of a barcode gap (p = 0.27).
Highlights
Podocarpaceae is a family of evergreen trees and shrubs that are sometimes cultivated as ornamentals in suitably warm climates
Mismatches between morphological/anatomical species circumscription and barcode sequences warrant further investigation as they may indicate the presence of cryptic species, introgression, or ancestral polymorphism followed by incomplete lineage sorting
The vast majority of barcode sequences generated for this study were of high quality (Figure 2)
Summary
Podocarpaceae is a family of evergreen trees and shrubs that are sometimes cultivated as ornamentals in suitably warm climates. Accurate identification of tropical forest trees, such as Podocarpaceae, is often very difficult. Sterile material of Podocarpaceae can usually be identified to genus using phyllotaxis and leaf form [3,4], accurate species identification often requires careful microscopic examination of internal [5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20] and external characteristics [21,22,23,24,25,26,27]. Proper use of the existing identification tools requires training in botanical terminology, skill in microtechnique, and familiarity with Podocarpaceae
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