Number of Myrtaceae pollen types reported in melissopalynological and pollen foraging studies in South America.

<p>Number of Myrtaceae pollen types reported in melissopalynological and pollen foraging studies in South America.</p

Pollen analysis of Australian honey

<div><p>Pollen analysis is widely used to verify the geographic origin of honeys, but has never been employed in Australia. In this study, we analysed the pollen content of 173 unblended honey samples sourced from most of the commercial honey producing regions in southern Australia. Southern Australian vegetation is dominated by <i>Eucalyptus</i> (Myrtaceae) forests and, as expected, most Australian honeys are palynologically dominated by <i>Eucalyptus</i>, while other important components include Myrtaceae taxa such as <i>Corymbia</i>/<i>Angophora</i> and the tribe Leptospermeae; plus Brassicaceae, <i>Echium</i>, <i>Macadamia</i>, and <i>Acacia</i>. An important feature of the honeys is the number of Myrtaceae pollen morphotypes per sample, which is generally high (mean = 4.6) compared to honeys produced outside of Australia, including <i>Eucalyptus</i> honeys produced in the Mediterranean region, and honeys produced in South America, which has its own rich indigenous Myrtaceae flora. In the latter regions, the number of Myrtaceae morphotypes is apparently generally ≤2. A high number of Myrtaceae morphotypes may be a feasible criterion for authenticating the origin of Australian honeys, since most Australian honey is produced by honey bees mainly working indigenous floral resources. Myrtaceae morphotype diversity is a convenient melissopalynological measure that could be applied even where detailed knowledge of the pollen morphology of the many component genera and species is absent. Palynological criteria developed in Europe for authenticating <i>Eucalyptus</i> honeys should not be relied upon for Australian honeys, since those criteria are not based on samples of Australian honey.</p></div

Numbers of pollen types and pollen concentrations.

<p><b>a</b>, Histograms of total number of pollen types per sample, and <b>b</b>, pollen concentration, on a log₁₀ scale, with Maurizio’s groups I-V [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0197545#pone.0197545.ref007" target="_blank">7</a>] delineated.</p

Principal component biplots of pollen types.

<p>Upper panel, numerically dominant types, 42% of variance explained by the first two axes; lower panel, numerically minor types, 31% of variance explained by the first two axes.</p

Myrtaceae pollen diversity observed in the honeys.

<p>36 distinct Myrtaceae morphotypes observed in the 173 honey samples, many unassigned below family level. Morphotypes 1–12, parasyncolporate grains with more or less well developed pore thickenings, broadly consistent with <i>Eucalyptus</i> species; morphotype 15, large grains, weakly oblate, approaching cubic or spheroidal shape, consistent with some <i>Corymbia</i>/<i>Angophora</i> species; morphotype 16, with short colpi not reaching the polar region, consistent with some members of the VACDH clade [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0197545#pone.0197545.ref052" target="_blank">52</a>]; morphotype 29, regulate grains possibly consistent with tribe Myrteae; morphotypes 30–32 and 34–35, consistent with tribes Leptospermeae and Chamelaucieae; morphotype 33, very small grain possibly consistent with <i>Tristania</i>. For brief descriptions, see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0197545#pone.0197545.s001" target="_blank">S1 Appendix</a>.</p

East-west comparison of Myrtaceae and Proteaceae morphotypes diversity.

<p>Histograms of number of Myrtaceae (green) and Proteaceae (blue) pollen morphotypes, for eastern (<b>a,b</b>) and southwestern (<b>c,d</b>) Australian honey samples.</p

Relationship between percent <i>Eucalyptus</i> pollen and total pollen concentration, in purportedly unifloral <i>Eucalyptus</i> honeys.

<p>Percent <i>Eucalyptus</i> pollen in 76 samples described by Australian beekeepers as derived solely from one or more <i>Eucalyptus</i> species (that is, unifloral, or in some cases bifloral <i>Eucalyptus</i> honeys), vs. total pollen concentration, plotted with a log₁₀ scale. For comparison, pink shading indicates the International Honey Commission’s criteria [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0197545#pone.0197545.ref032" target="_blank">32</a>], based on percent <i>Eucalyptus</i> pollen (>83%) and range of total pollen concentration (9000–54,000 pollen grains/g), for acceptance of a honey as a unifloral <i>Eucalyptus</i> honey. Comparatively few Australian <i>Eucalyptus</i> unifloral honeys plot in this region.</p

Number of Myrtaceae pollen types reported in melissopalynological studies in Mediterranean countries.

<p>Number of Myrtaceae pollen types reported in melissopalynological studies in Mediterranean countries.</p

Myrtaceae morphotype diversity and total percent Myrtaceae pollen.

<p>Linear correlation between number of Myrtaceae morphotypes per honey sample, and percent Myrtaceae pollen (the sum of <i>Eucalyptus</i>, <i>Corymbia</i>/<i>Angophora</i>, Leptospermeae and Myrtaceae undif.) within the sample, is low and statistically insignificant (<i>n</i> = 173, r = -0.015. T-value of -0.193 is less than a critical threshold t_critical = 1.65, testing the hypothesis that the correlation coefficient equals zero. Pink bar indicates approximate region in which Mediterranean-region <i>Eucalyptus</i> honeys would plot, with gradient indicating that <i>Eucalyptus</i> pollen % in Mediterranean honeys can vary from 0 to ~100%, but consistently with only 1–2 Myrtaceae pollen morphotypes. Comparatively few Australian honeys plot in this region.</p

Location of the 173 honey samples within Australia.

<p>The data used to produce this figure can be found in the <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0197545#pone.0197545.s003" target="_blank">S1 Table</a>.</p