<i>Premna vietnamensis</i> (Lamiaceae, Premnoideae), a distinct new species from the Central Highlands of Vietnam

<div><p><i>Premna vietnamensis</i>, a distinct new species which is endemic to Gia Lai Province in Central Highlands of Vietnam, is described and illustrated. It is characterized by its calyx tube bearing a semi-globose fleshy appendage, which has not been reported before from all known congeneric taxa, as well as from the Lamiaceae. A phylogenetic analysis of the whole Lamiaceae based on a sampling including representatives from all 12 currently recognized subfamilies confirmed the placement of this new species within <i>Premna</i> of the Premnoideae. Morphologically and geographically, <i>P</i>. <i>vietnamensis</i> is most similar to <i>P</i>. <i>stenobotrys</i>, but differs significantly in many aspects.</p></div

Comparisons of calyx morphology of <i>Premna vietnamensis</i> (A), <i>Vitex gamosepala</i> (B), and <i>Scutellaria</i> L. (C).

<p><b>A,</b> An inflorescence of <i>P</i>. <i>vietnamensis</i> showing the semi-globose fleshy appendage on calyx tube (indicated by the arrow). <b>B,</b> A cyme of <i>V</i>. <i>gamosepala</i> showing the fleshy calyx lob (indicated by the arrow). <b>C,</b> An infructescence of <i>S</i>. <i>indica</i> L. showing the typical dorsal shield on the calyx of <i>Scutellaria</i> species (indicated by the arrow).</p

Illustration of <i>Premna vietnamensis</i>.

<p><b>A</b>, A flowering branchlet. <b>B</b>, An infructescence. <b>C</b>, Flowers (left: adaxial view; right: abaxial view). <b>D</b>, Calyces (left: lateral view; middle: apical view; right: inside view after dissection). <b>E</b>, A mature fruit (left) and its pyrene (right). <b>F</b>, Longitudinal section (upper) and cross section (lower) of fruits.</p

Specimens of <i>Premna vietnamensis</i> (A, B) and <i>P</i>. <i>stenobotrys</i> (C, D).

<p><b>A,</b> Branchlets, leaves and inflorescences of <i>P</i>. <i>vietnamensis</i> taken from <i>L</i>.<i>K</i>. <i>Bien 830</i> (HN). <b>B,</b> An inflorescence of <i>P</i>. <i>vietnamensis</i> taken from <i>VK 4457</i> (HN) showing dense golden hairs on branchlets, petioles, and peduncles. <b>C,</b> Isotype of <i>P</i>. <i>stenobotrys</i>, <i>P</i>.<i>A</i>.<i>Pételot 1179</i> (HNU). D, An infructescence of <i>P</i>. <i>stenobotrys</i> taken from <i>P</i>.<i>A</i>.<i>Pételot 1179</i> (HNU).</p

Distribution of <i>Premna vietnamensis</i> in Gia Lai Province of Vietnam.

<p>Distribution of <i>Premna vietnamensis</i> in Gia Lai Province of Vietnam.</p

Morphology and anatomy of <i>Premna vietnamensis</i>.

<p><b>A</b>, Adaxial view of a fruiting branchlet. <b>B</b>, Abaxial view of a fruiting branchlet. <b>C</b>, Adaxial view of a leaf apex. <b>D</b>, Abaxial view of a leaf apex. <b>E</b>, Flower. <b>F</b>, Infructescence and mature fruits with persistent calyces. <b>G</b>, Radial (upper) and tangential (lower) dissections of flowers. <b>H</b>, Vertical dissections of a fruit. <b>I</b>, Equatorial (upper) and polar (lower) view of a pyrene. <b>J</b>, A cross section of a pyrene. All arrows pointed to the fleshy appendage on calyx tube. Ruler scale in F–J is 1 mm.</p

Bayesian 50% majority-rule consensus tree of Lamiaceae based on the combined cpDNA (<i>matK</i> + <i>rbcL</i> + <i>trnL-F</i>) data set, with gaps treated as simple indels.

<p>The topology of the ML tree is congruent with the BI tree. The 12 subfamilies of Lamiaceae are marked by different colors. Numbers above and below the branches are Bayesian posterior probabilities (PP) and maximum parsimony bootstrap values (BS), respectively. The bold lines indicate the PP = 1.00 and simultaneously BS = 100. The absent numbers mean the support value ≤ 65% for BS or 90% for PP. The symbol “*” marks the phylogenetic position of <i>P</i>. <i>vietnamensis</i> represented by three accessions. A single generic name indicates that the combined sequences were pooled from different species of the genus. Multiple accessions of the same species are numbered according to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0195811#pone.0195811.s001" target="_blank">S1 Table</a>.</p

Premna vietnamensis.

<p><b>A</b>, Habitat and habit. <b>B</b>, A branch and a branchlet with inflorescence. <b>C</b>, Leaf bases and petioles.</p