Vincetoxicum tmoleum, Boissier (1844: 38)

Güven, Seher, Makbul, Serdar, Coskuncelebi, Kamil & Pinar, Nur Münevver, 2015, Pollinarium morphology of Vincetoxicum (Apocynaceae: Asclepiadoideae) in Turkey, Phytotaxa 230 (1), pp. 22-38 : 30-32

V. tmoleum Boissier (1844: 38) :

Pollinium ovate, 259.1 (±7.28) × 149.8 (±5.02) μm; pollen cells 40.5 (±2.76) × 27.8 (±3.07) μm, inaperturate; ornamentation tectate-perforate, rugulate. Corpusculum ovate, 223.7 (±6.73) × 108.6 (±5.21) μm. Caudicle attached to the corpusculum sub-apically and to the pollinium sub-basally, 113.4 (±4.63) × 19.4 (±1.30) μm ( Fig. 11 ).

Numerical analysis

The dendrogram resulting from the cluster analysis (based on 11 palynological characters of 20 samples representing ten taxa) is given in Fig. 12 . As seen in the dendrogram, all investigated taxa fall into two major clusters at 98.75% dissimilarity level. The first cluster, labeled “a”, comprises nine samples belonging to V. canescens subsp. canescens , V. canescens subsp. pedunculata , V. parviflorum , and V. tmoleum . The second cluster, labeled “b”, includes the remaining eleven samples (representing six taxa) of Turkish Vincetoxicum . The cophenetic correlation coefficient of the dendogram is 0.86. Cluster “a” is characterized by ovate or elliptical pollinia with width/length ratios ranging from 0.58 to 0.65. Cluster “b” is represented by clavate or obovate pollinia with width/length ratios ranging from 0.30 to 0.47.

Cluster “a” is divided into two subclusters, linked to each other at a 83.75% dissimilarity level. The first subcluster contains seven different populations in total, representing two subspecies of V. canescens , as well as V. tmoleum . V. canescens subsp. canescens and V. canescens subsp. pedunculata were noted as phenetically similar taxa by Browicz (1978). These two taxa, previously distinguished from one another based on peduncle length, are also similar in palynological traits, but can be distinguished by pollinium length (see key below). V. canescens and V. tmoleum share similar yellow or greenish flowers ( Browicz 1978), but can be distinguished by stems decumbent and indumentum grey-tomentose in the former ( Browicz 1978). Our results demonstrate that the two can also be distinguished by palynological characters, including the length of the corpusculum.

Vincetoxicum parviflorum , a member of the second subcluster of cluster “a”, is easily distinguished from the rest of the three taxa in the cluster by the pollinaria smaller, the pollinia elliptical, the corpuscula oblong, and the pollen gemmate. Browicz (1978) suggested that V. parviflorum could be a variety of V. fuscatum with small-flowers, but our palynological results are not in accordance with this view, supporting instead Boissier (1875), who considered the taxa distinct at the species level. In fact, Boissier (1875) noted that these two taxa differ from each other in a number of morphological characters related to the stem and flower ( Boissier 1875). For example, V. fuscatum is characterized by a cup-shaped, 5-parted corona, the scales of which exhibit intermediate short teeth and are nearly equal with the gynostegium length. In contrast, in the smaller flowers of V. parviflorum , the corona is deeply 5-parted and the corona scales are triangular-ovate and quite shorter than gynostegium. Additionally, while V. parviflorum exhibits densely branched stems, V. fuscatum exhibits simple or few-branched stems ( Boissier 1875).

The second major cluster is also divided into two subclusters. Subcluster “d” consists of four populations belonging to V. fuscatum subsp. boissieri and V. scandens , while subcluster “c” includes V. funebre , V. fuscatum subsp. fuscatum , V. hirundunaria subsp. hirundinaria , and V. speciosum . Browicz (1978) recognized two phenetically similar subspecies of V. fuscatum — subsp. boissieri and subsp. fuscatum —distinguished only by corolla indumentum. In contrast to Browicz (1978), these two subspecies were recognized as separate species by Pobedimova (1952) (as Antitoxicum boissieri (Kusnezov) Pobedimova (1952: 680) [= V. fuscatum subsp. boissieri ] and Antitoxicum minus (C.Koch) Pobedimova (1952: 687) [= V. fuscatum subsp. fuscatum ]). Although the general appearance and corona structure of V. fuscatum subsp. boissieri and V. fuscatum subsp. fuscatum are very similar ( Pobedimova 1952), Pobedimova (1952) suggested that these two taxa be classified under different series based on the pubescence of the inner surface of corolla. As seen in the dendrogram resulting from our cluster analysis, the two subspecies emerged in different subclusters based on palynological features, including the size of pollinia, corpuscula, and caudicles. Thus, our results support Pobedimova’s (1952) view, but further morphological and molecular studies are required to better understand the evolutionary relationship of these phenetically similar taxa.

In subcluster “c”, samples of V. speciosum differed from the other three taxa on the basis of the long pollinia (341.6 ±11.42 μm) and the low pollinium width/length ratio (0.30). Interestingly, the phenetically rather different species V. funebre (corollas dark purple and stems erect, to 70 cm) and V. hirundinaria subsp. hirundinaria (corollas white or pale yellow and stems twining, ca. 120 cm) ( Browicz 1978) emerged in the same subcluster. This is likely the result of similarities in the size, shape, and surface ornamentation of their pollinia.

An ordination derived from PCA based on 11 palynological traits is given in Fig. 13 . The eigenvalues of the first, second, and third component in percentages are 66.17%, 19.97%, 6.58%, respectively ( Table 3). The first three components explain 92.72% of the total variation among the investigated taxa, suggesting that the shape of the pollinium and corpusculum, the size and surface ornamentation of pollen cells, and the size of the corpusculum and caudicle are valuable palynological characters for grouping the investigated taxa.

Figures

FIGURE 11. Vincetoxicum tmoleum (Güven 52). a. Pollinarium (LM); b. Pollinarium (SEM); c. Pollen cells; d. Ornamentation.

FIGURE 12. Dendrogram resulting from cluster analysis-UPGMA (X2: Pollinium shape, X5: Pollen ornamentation.

FIGURE 13.Ordination resulting from PrincipalComponentsAnalysis (PCA) of 20samples belonging toten taxa of Turkish Vincetoxicum, based on 11 palynological traits.