An Anatomical Study of Scilla (Scilloideae) Section Chionodoxa and Scilla bifolia in Turkey

Abstract

In the present study Scilla luciliae, S. forbesii, S. sardensis, S. siehei, Scilla x allenii and S. bifolia are compared anatomically. Some differences have been found in root, scape, and leaf anatomy of the taxa, and commented. S. luciliae, S. forbesii, S. sardensis and S. siehei have a metaxylem at the center of the root, others have 3-4 number metaxylem. Vascular bundles in two row in S. luciliae and S. forbesii in a single row in S. sardensis, Scilla x allenii and S. bifolia though in three rows in S. siehei. Aerenchyma tissue is present in mesophyll of five taxa leaf except S. sardensis. The anatomical variations in the taxa have been investigated by means of numerical methods (Analysis of variance and Pearson correlation). By the analysis of the investigated taxa from 12 anatomy related characters, it has been also found that the results from numerical analysis of anatomy characters can provide additional evidences, which correspond to the anatomy for the recognition of the taxa.

INTRODUCTION

Chionodoxa and Scilla are close related genera of Liliaceae. Chionodoxa and Scilla transferred into subfamily Scilloideae of Asparagaceae family within the scope ofAPG III (Angiosperm Phylogeny Group) system (APG III, 2009; Chase et al., 2009; Reveal and Chase, 2011). In Flora of Turkey and the East Aegean Islands Volume 8, Scilla and Chionodoxa were evaluated and revised as two separate genera (Davis, 1984). According to the last world monocot checklist Scilla sect. Chionodoxa is represented with six species worldwide, 3 species of those are native to Turkey (S.luciliae, S. sardensis, S. forbesii, one species to Cyprus (S. lochiae) and 2 species to Crete (S. nana and S.albescens) (Govaerts, 2014). Davis (1984) treats S. siehei as a synonym of S. forbesii. In the scope of a Ph.D. thesis study by the first author the taxa of S.sect. Chionodoxa in Turkey have been revised between 2004-2010 based on morphological, molecular, and ecological data and the reproductive system (Yildirim, 2010). According to these results, S. sect. Chionodoxa is represented in Turkey by S.luciliae, S.forbesii, S.sardensis and S.siehei. Moreover, a natural hybrid (Scillaxallenii) between S. siehei and S. bifolia was found in this study. Except for S. bifolia, all other species are local endemic plants. Although, S.siehei (only growing in Nif Mountain), Scilla x allenii (only growing in Nif Mountain), S.sardensis (only growing in Mahmut Mountain) and S.luciliae (only grows in Bozdag Mountain) are distributed along the Bozdag Mountain series in Izmir Province, S.forbesi (only grows in Babadag Mountain) is distributed in Mugla. However, Scilla bifolia is a very common species distributed in several countries, Turkey, the Caucasus, Iraq, Iran, Syria along the danube river up to central Europe.

In this paper, the species of S. sect. Chionodoxa (S. luciliae, S. forbesii, S. sardensis and S. siehei), S. bifolia and the natural hybrid S. allenii are compared on the base of some anatomical features.

MATERIALS AND METHODS

Taxa have been collected from the following natural habitates by Hasan Yildirim during field studies for his thesis (Table 1).

[Table Omitted. Please see PDF.]

Scilla siehei, S. forbesi, S. sardensis, S.luciliae and Scilla x allenii are local endemic plants that are only known from type localities. Each of these taxa have just one single population. For this reason, we used material obtained from subpopulations at different altitudes from each taxon population. Although, S.bifolia is a very common species, we used its Nif Mountain population, because of the hybrid taxon Scilla x allenii occuring nearby.

A total of 30 individuals collected from subpopulations at different altitudes were used. For anatomical studies plant specimens were fixed in 70% ethanol. The paraffin method (Algan, 1981) was used for preparing the cross-sections of root, scape and leaves for each sample. Roots of the same diameter have been used for cross-sections. Transverse sections 15-20 m were made using a sliding microtome. Slides stained with safranin-fast green. Slides were photographed with motorized Leica DM 300 microscope. Species root, stem, and leaf cell size were measured using an ocular-micrometer. Minimum, maximum, mean, and standart deviation were determined.

RESULTS AND DISCUSSION

Root

All taxa show a one layered rhizodermis. Scilla bifolia has a 11-13 layered cortex, whereas the others have only a 6-8 layered root cortex. Scilla luciliae, S.forbesii, S.sardensis and S.siehei have a metaxylem vessel in the center of the root, while others have 3-4 metaxylem vessels. The endodermis cell wall of all taxa is thickened on all 4-sides o-type endodermis. Scilla luciliae, S.forbesii, and S.siehei have five xylem strands, while S.sardensis, Scilla x allenii and S.bifolia have six xylem strands (Figure 1 and 2). Also, root cross-sections of S.siehei, Scilla x allenii and S.bifolia have raphide crystals in cortex.

[Figure omitted. Please see PDF.]

[Figure omitted. Please see PDF.]

Scape

The cuticle layer is very thick in Scilla luciliae, S. sardensis, S. siehei, S. bifolia and Scillax allenii. However S. forbesii has a thinner cuticle than the other species. A single layered epidermis forms projections in the transversal section that form longitudinal ribs in all taxa except Scilla x allenii. The cortex is 4-6 layered in all taxa. Vascular bundles are arranged in two circles in S. luciliae and S.forbesii but in a single circle in S.sardensis, Scilla x allenii and S.bifolia, and in three circles in S. siehei. The pith area has a disjunction in S. luciliae, S. forbesii, S.sardensis, Scilla x allenii and S. bifolia (Figure 3 and 4). S. forbesii, S. sardensis, Scillax allenii and S. bifolia taxa have needle-shaped raphide crystals in scape cross-sections (Figure 6).

[Figure omitted. Please see PDF.]

[Figure omitted. Please see PDF.]

[Figure omitted. Please see PDF.]

[Figure omitted. Please see PDF.]

Leaf

A cuticle layer is present on both surfaces in all taxa. The abaxial cuticle is thicker than the adaxial one. A prominent stomatal chamber is present in five taxa, except for Scilla sardensis. S. luciliae and S. siehei, which have palisade and spongy parenchyma, others have one type mesophyll cell. Aerenchyma tissue is present in the mesophyll in all taxa except for S. sardensis. A bundle sheat is present in leaf of all taxa (Figure 5). Scilla forbesii, S. sardensis and Scilla x allenii taxa have raphide crystals (Figure 6, Table 2).

[Table Omitted. Please see PDF.]

Statistical analysis

The anatomical measuments of the investigated taxa were shown in Table 2. Difference relevance among the investigated taxa was evaluated by analysis of variance (Regression Analysis) and Pearson correlation (Correlation). The statistical analysis of the results is provided in Tables 3 and 4.

[Table Omitted. Please see PDF.]

[Table Omitted. Please see PDF.]

According to both methods of analysis, the differences among the investigated taxa are shown as B-D, B-E, C-F and D-F in Table 2 and Table 3, they are significant at level of 0.01P and 0.05P. Furthermore, a significant difference has been found at levels of 0.05 between A and B according to Table 3 based of Pearson correlation method (Correlation).

In this study, the species of Scilla sect. Chionodoxa, the closely related species S. bifolia and the natural hybrid association between S. bifolia and S. siehei (Scilla x allenii) were compared anatomically.

Considering root cross-sections, some similarities and differences were observed in all taxa. Satil and Akan (2006) have observed metaxylem and 4-5 xylem strands in S.mesopotamica, similar to those in S. luciliae, S.forbesii, and S. siehei. Endodermal thickenings are present in S.mesopotamica too. Crystals are a constant characteristic of the group. The shape and location of the crystals in plants are very important for taxonomic studies (Metcalfe and Chalk, 1983; Yentür, 1995; Fahn, 1990). Needle-shaped raphide crystals were found in roots of S.siehei, Scilla x allenii and S.bifolia, but they were absent in other studied taxa. S.mesopotamica has raphide crystals in root cross-section (Satil and Akan, 2006).

According to Satil and Akan (2006), 7-10 number of vascular bundles in a row in S.mesopotamica is similar to S. sardensis, Scilla x allenii and S.bifolia taxa. Vascular bundles in three rows of S.peruviana are similar to S.siehei, and those arranged in two of S. verna, S. luciliae and S.forbesii (Rubim et al., 2013). Scilla x allenii’s scape shape is less protruding from others. Needle shaped raphide crystals present in S.forbesii, S.sardensis, Scilla x allenii and S.bifolia. S.mesopotamica’s scape have raphide crystals too (Satil and Akan, 2006).

The presence of cavities and a homogeneous mesophyll is the rule in the taxa of Hyacinthoides and Scilla (Rubim et al., 2013). In leaf anatomy, stomatal cavity present under the stomata in five taxa, except for S. sardensis. Rubim et al. (2013) has reported that S. monophyllos, S. odorata, S.ramburei, S. verna, S. merinoi. In our study, S.forbesii, S.sardensis, Scilla x allenii and S. bifolia taxa have homogeneous mesophyll, while S. luciliae and S. siehei species have heterogeneous mesophyll. Aerenchyma cavities present in mesophyll in leaves of five taxa except S. sardensis. Cavities have been observed in leaves of S.monophyllos, S. odorata, S. ramburei, S. verna, S. merinoi, S. hyacinthoides, S. lilio-hyacinthus (Rubim et al., 2013) and S. mesopotamica (Satil and Akan, 2006). Bundle sheat is present in leaf of all studied taxa. Satil and Akan (2006) have observed bundle sheat in S. mesopotamica, Also they have raphide crystals in leaf cross section of the latter which are similar to S. sardensis and Scilla x allenii taxa.

As shown in Table 3 and Table 4, there are important correlations between S. siehei and S.bifolia, which are the two closely related taxa. Scilla x allenii is hybrid taxa between S. siehei and S. bifolia. It is mentioned that Chionodoxa and Scilla. are closely related genera of Liliaceae (Mathew, 1987). Also, according to the statistical results found, there is a considerable relation among the species of the two genera, at the level of P<.01 and P<.05. It has been also found that the results from numerical analysis of anatomy characters can provide distinct evidences, which correspond to the anatomy for recognition of the taxa. By the analysis of the investigated taxa from 12 anatomy characters, it has been determined that metaxylem number in roots and vascular bundle row number in scapes are the best character pairs that represent the variations in them.

Consequently Scilla section Chionodoxa and S. bifolia thought to have originated of the section are similar in many anatomical characters. Meanwhile, some characters such as metaxylem vessel number in roots, vascular bundle row number in scapes, and mesophyll structure in leaves, are useful to taxonomically distinguish these taxa.

ACKNOWLEDGEMENTS

This study has been supported by the project of Doctorate thesis of first author [the name of this thesis: Taxonomy, Ecology and Reproduction of Genus Chionodoxa Boiss. (Liliaceae)]. We thank the Research Fund of Ege University (project number: 2006 FEN 052), and the Turkish Research Council (TUBITAK) (project number: 106T598) for providing financial support.

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