INTRODUCTION 
The genus Allium L. includes over 800 species, 15 subgenera and more than 70 sections (Friesen et al., 2006; Fritsch et al., 2010) of herbaceous perennial plants with natural distributions in the Northern Hemisphere (Stearn, 1978, 1980; Friesen, 1988; Friesen et al., 2006; Fritsch and Abbasi, 2009). The genus Allium was previously classified as a member of the Lilliaceae family and then Alliaceae, subfamily Allioideae Herb. (Fay and Chase, 1996). Recently Allium has been placed within Amaryllidaceae (APG III, 2009). The genus is characterized by the presence of bulbs enclosed in membranous (sometimes becoming fibrous) tunics, free or almost-free tepals and often a subgynobasic style (Friesen et al., 2006). The diversity of Allium is greatest in Southwest and Central Asia and the Mediterranean region, and there is a second smaller center of diversity in North America (McNeal, 1992; Friesen et al., 2006; Nguyen et al., 2008). 
Several criteria have been used in taxonomic classification of Allium. Some characters have proved useful at subgeneric and sectional levels, including the structure and shape of rhizome and bulb, and anatomical features of root, leaf, scape, ovary, septal nectaries and seed (De Wilde-Duyfjes, 1976; Fritsch, 1992, 1993; Kruse, 1992; McNeal, 1992; Friesen et al., 2006; Gurushidze et al., 2008; Nguyen et al., 2008; Choi and Cota-Sánchez, 2010; Celep et al., 2012). Many other characters are diagnostically important and commonly used in species descriptions. Scanning electron microscopy (SEM) has greatly improved the taxonomy of the genus, 
© Polish Academy of Sciences and Jagiellonian University, Cracow 2014 
facilitating studies of the ultrasculpture and orna-mentation of the seed coat (Pastor, 1981; Kruse, 1984, 1992; Èešmedžiev and Terzijski, 1997; Fritsch et al., 2006; Neshati and Fritsch, 2009; Celep et al., 2012; Choi et al., 2012), pollen grains (Güler and Pehlivan, 2006; Namin et al., 2009), bulb coats (De Wilde-Duyfjes, 1976; McNeal, 1982, 1992; Choi and Oh, 2011), floral structures (Choi et al., 2011) and leaf epidermal cells (Garbari et al., 1979; Krahulec, 1980; Choi et al., 2004; Choi and Oh, 2011). 
The bulb plays an important role in species identification within the genus Allium. Bulb structure, shape and size and especially the texture of the outer bulb tunic play a great part in species diagnosis (De Wilde-Duyfjes, 1976; McNeal, 1982; Speta, 1984; Pastor and Valdés, 1986; McNeal and Jacobsen, 2002). Bulb tunic ornamentation has been used to elucidate the relationships among North American species (McNeal, 1992) and East Asian species (Choi and Oh, 2011). The bulb tunic develops through differential lignification of the inner and radial cell walls of the adaxial epidermis of the uppermost foliage leaf (McNeal and Ownbey, 1973). Depending on the lignification processes, two bulb coat types have been dis-tinguished (fibrous-reticulate, smooth nonreticulate), and the usefulness of tunic cell pattern and shape in distinguishing particular species has been noted (McNeal, 1992). Nevertheless, the use of bulb tunic ornamentation and cell pattern for identifying Allium species is rarely considered, especially in reference to comprehensive classification of the genus. 
What is the relationship between micromorphology and the molecular data used to reconstruct Allium phylogeny? The bulb tunic ornamentation of some species has not been investigated previously. In this work I examine these microstructures in order to assess their usefulness for the classification of Allium proposed by Friesen et al. (2006), and specifically, to study the diversity of bulb tunic cell pattern and ultrasculpture in selected Allium species, to assess the diagnostic value of these char-acters at different taxonomic levels (species, section, subgenus), and to consider the results in relation to the recent intrageneric classification. 
MATERIALS AND METHODS 
The ultrasculpture of the bulb tunics of 46 selected Allium species representing 10 subgenera and 21 sections was examined by scanning electron microscopy (SEM) (JEOL JSM-5410 and NORAN Vantage) at 15 kV accelerating voltage. The samples were sputter-coated with gold (for details see Rola, 2012). The observations used 92 herbarium speci-mens (two of each species when available, two sam-ples from one specimen when not). The specimens are housed in KRA (Jagiellonian University, Cracow). When possible the specimens were selected from different parts of the species' distribution range. Next, epidermal peels of the inner surface of the bulb tunic of each species (except for species with typical reticulate or crustaceous outer tunics) were examined by light microscopy (LM) to observe their cell shape patterns. Table 1 lists the examined species together with herbarium collection data (when labels were legible). The terminology describing bulb tunic ultrasculpture follows De Wilde-Duyfjes (1976) and McNeal (1992). 
RESULTS AND DISCUSSION 
The diversity of bulb tunic texture, ultrasculpture and cell patterns of the studied Allium species are presented in Figures 1–7 and Table 1. In most cases the texture of bulb tunics was membranous or papery (Tab. 1). In some it was fibrous, and the fibers were more or less parallel (e.g., A. moschatum, Fig. 4a) or formed a reticulate structure (taxa of 3 subgenera: Reticulatobulbosa, Butomissa and Anguinum, Figs. 2h,i, 3a, 4b–g). In some species, mainly from sub-genus Amerallium, the structure of outer tunics was chartaceous or crustaceous with distinctive ultra-sculpture visible under SEM (e.g., Fig. 2d–f). These characters of the outer bulb tunic apparently are of high diagnostic value. I determined some species-specific and subgenera-specific characters for which variation between specimens representing the same species is negligible; specimens from different geographical areas (Tab. 1) showed uniform outer bulb tunic ultrasculpture and cell pattern. These characters are stable and therefore can be successfully used in species descriptions and determination keys. 
Some taxa had numerous calcium oxalate crystals visible by LM, or in the form of verrucae under SEM (Tab. 1). The crystals are actually intracellular, embedded in the cell mesophyll (Prychid and Rudall, 1999); that is why only their shapes were visible by SEM. This study supports Jaccard and Frey's (1928) suggestion that crystal types are useful for determining some species but not for the whole systematics of the genus. In contrast, Chartschenko (1932) distinguished 8 types and forms of calcium oxalate crystals in Allium and remarked that they play an important role in phylogenetic systematics. However, his classification of certain species differs from the recent intrageneric classification (Friesen et al., 2006). I found calcium oxalate crystals in the outer bulb tunics of 23 of the examined species (Tab. 1), but no specific types of oxalate crystals were characteristic of subgenera or sections. 
In the present work the main differences in bulb tunic ultrasculpture and cell pattern were at species level; specific characters for only a few subgenera were identified. Convergent evolution can lead to sim
TABLE 1. Main characteristics of outer bulb tunics of examined Allium species, with herbarium data. Subgenera and sections follow Friesen et al. (2006) and Nguyen et al. (2008) 
TABLE 1. Cont. TABLE 1. Cont. TABLE 1. Cont. 
ilarity of characters in taxonomically different species, leaf epidermal pattern (Krahulec 1977, 1980). Some and sometimes there is a great variation of ultrasculp-bulb tunic characters might also be modified by enviture within subgenera. Such a case was reported for ronmental conditions, and some structures may be 

F
i
g
. 
1
. Ultrasculpture of outer bulb tunic (inner surface) of examined Allium species. (a
) Allium acutiflorum, 
(b
) A. ampeloprasum, (c
) A. atroviolaceum, (d
) A. polyanthum, (e
) A. scorodoprasum subsp. rotundum, 
(f
) A. scorodoprasum subsp. scorodoprasum, (g
) A. sphaerocephalon, (h
) A. vineale, (i
) A. carinatum, (j
1
, j
2
) A. flavum, 
(k
) A. melanantherum, (l
1
, l
2
) A. oleraceum, (m
) A. paniculatum, (n
) A. stamineum. Bar = 50 μm. 

adaptations to local habitat factors (Krahulec, 1980; hexagonal (Fig. 1e,g,i,m) or smooth to reticulate McNeal and Ownbey, 1982; McNeal, 1992). (Fig. 1b–d,k,n). Eight taxa of this subgenus had hexagonal cells with numerous or less numerous calcium
Following are findings for particular subgenera. 
oxalate crystals (Figs. 5a,d,e–g,i, 6a,b). The other species had elongated cells. Calcium oxalate crystals
Allium subgenus Allium 
were fairly common in the bulb tunics of members of The species referred to this subgenus were charac-this subgenus (Tab. 1; compare with data on crystals terized by considerable variation. Bulb tunic ultra-in epidermal tissue in Mathew, 1996). Only A. vineale sculpture was striate with distinct ribs (Fig. 1a,h,j,l), showed no crystals. The inner surface of the outer 

F
i
g
. 
2
. Ultrasculpture of outer bulb tunic (inner surface) of examined Allium species. (a
1
, a
2
) Allium ursinum, 
(b
) A. pendulinum, (c
) A. triquetrum, (d
) A. chamaemoly, (e
) A. moly, (f
1
, f
2
) A. roseum, (g
1
, g
2
) A. subhirsutum, 
bulb tunic of A. ampeloprasum was composed of elongated cells with numerous oxalate crystals (Fig. 5b); in contrast, De Wilde-Duyfjes (1976) observed hexagonal cells in African specimens. My study showed subtle differences between the outer bulb tunics of A. ampeloprasum and A. atroviolaceum. The latter differs in having distinct reticulate fibrous outer tunics with prominent ribbing (Fig. 5c), which are absent in A. ampeloprasum (Fig. 5b) (see also descriptions in Vvedensky, 1935; Wendelbo, 1985). Allium sphaerocephalon showed two types of ultrasculpture and cell pattern depending on bulb tunic texture. In membranous bulb tunics, the cell pat-tern was hexagonal to rectangular with numerous oxalate crystals (Fig. 5g); more coriaceous bulb tunics had striate ultrasculpture with rectangular elongated cells. Similar observations were made by De Wilde-Duyfjes (1976), who presented three types of bulb tunic cell pattern. Allium vineale bulb tunics showed a characteristic ribbed structure with elongated cells, as also found by De Wilde-Duyfjes (1976) and McNeal and Jacobsen (2002), but high magnification also revealed papillary structure of the ribs (Fig. 1h). Allium oleraceum had distinct ultrasculpture with longitudinal ribs (compare with illustration in Aedo, 2013), with additional ultrasculptural details: ribs covered with spiral protrusions (Fig. 1l). The outer bulb tunic of A. paniculatum was membranous, with hexagonal cells (Fig. 6a), similar to the description from De Wilde-Duyfjes (1976), who reported, however, that the outermost bulb tunic leaf had longitudinal ribs, not observed here. Allium stamineum had outer bulb tunics without nerves, consistent with the description from Vvedensky (1935) but contradicting Wendelbo (1985); its numerous calcium oxalate crystals (Fig. 6b) gave it a specific ultrasculpture visible by SEM (Fig. 1n). 
Allium subgenus Amerallium 
This subgenus showed the most distinctive structures, with great diversity of outer bulb tunic ultrasculpture. 

F
i
g
. 
3
. Ultrasculpture of outer bulb tunic (inner surface) of examined Allium species. (a
) Allium ramosum, (b
) A. cepa, 
(c
) A. fistulosum, (d
) A. sibiricum, (e
-
1
, e
-
2
) A. schoenoprasum, (f
) A. atropurpureum, (g
) A. nigrum, (h
) A. monanthum, 
Species-specific differences were recorded and cer-tain patterns were characteristic for particular species. The representative of section Arctoprasum – 
A. ursinum – showed a distinct type of cell pattern with elongated cells (Figs. 2a, 6c). A similar cell arrangement was observed in other members of sub-genus Amerallium from North America, for example 
A. lemmonii S.Watson (McNeal, 1992) and A. punc-tum L.F. Hend. (McNeal and Jacobsen, 2002), but in those cases the ultrasculpture showed thick lignified cell walls (McNeal, 1992). Allium pendulinum had curved cells with sinuate cell walls (Figs. 2b, 6d), with ultrasculpture somewhat resembling that reported by McNeal (1992) for North American taxa of this sub-genus: A. tribracteatum Torr. and A. nevadense 
S. Watson. Allium triquetrum did not have distinct ultrasculpture and its cell pattern consisted of rough-ly regular parallelograms (Fig. 6e). Similar observations were made by Aedo (2013). Allium chamae-moly had characteristic rhomboidal ultrasculpture (Fig. 2d) visible even at low magnification, as also reported by Aedo (2013). The pattern in A. moly was similar to A. pendulinum but the walls were much thicker (Figs. 2e, 6f). In A. roseum the inner layer of the bulb coat has been described as pitted and sclerified (Coste and Flahault, 1906; De Wilde-Duyfjes, 1976; Pastor and Valdés, 1983; Kollmann, 1984). Previous reports indicated finely sinuate cell walls (De Wilde-Duyfjes, 1976); in my study additional ultrasculptural details were visible (Fig. 2f). In fact the pitted structure of outer bulb tunics results from semilunar tubercular appendages clearly visible under SEM (Fig. 2f). All examined specimens of 
A. subhirsutum had sinuous cell walls in which no two cells appeared to have the same shape (Figs. 2g, 6g). Similar observations were made by De Wilde-Duyfjes (1976) but she found that three subspecies differ in the bulb tunic cell pattern; two of them, 
A. subhirsutum subsp. subvillosum and subsp. spathaceum, proved to have sinuous cells. 

F
i
g
. 
4
. Ultrasculpture of outer bulb tunic (inner surface) of examined Allium species. (a
) A. moschatum, (b
) A. inconspicuum, (c
) A. trachyscordum, (d
) A. flavidum, (e
) A. lineare, (f
) A. splendens, (g
) A. strictum, (h
) A. ochroleucum, 
Species of this subgenus are distributed mainly in the Mediterranean area, but a number of species with similar characters occur in North America (Badr and Elkington, 1978). The bulb tunic ultrasculpture of North American representatives of subgenus Amerallium has been examined and deemed valuable in elucidating relationships among the North American species (McNeal, 1992). The native North American taxa of subgenus Amerallium were found to be a well-supported monophyletic clade, sister to the Old World taxa (Nguyen et al., 2008). Scape anatomi-cal characters have also indicated close relationships between Old World and New World species of sub-genus Amerallium (Fritsch, 1993). The species examined during my study showed great variation of bulb tunic ultrasculpture and certain patterns proved to be characteristic for particular species. The ultrasculpture pattern of North American representatives has also been found to be species-specific (McNeal and Ownbey, 1982; McNeal, 1992; McNeal and Jacobsen, 2002), while a special type of leaf anatomy, scape anatomical structures and hypodermal laticifers in bulb scales are constant and characteristic for the whole subgenus (Huang and Sterling, 1970; Fritsch, 1988, 1993). 
Allium subgenus Anguinum 
Allium victorialis and A. tricoccum were characterized by fibrous and reticulate tunics (Fig. 2h,i). The bulb tunic creates a specific reticulum structure consisting of elongated cells. This result confirms previously published reports (e.g., Pastor and Valdés, 1983; Xu and Kamelin, 2000; Aedo, 2013). A similar arrangement has been observed among other species from Korea and northeastern China representing the same sister group of species, belonging to subgenus Anguinum: A. microdictyon Prokh. and A. ochotense Prokh. (Choi and Oh, 2011). 

F
i
g
. 
5
. 
Cell pattern of outer bulb tunic (inner surface) of selected Allium species. (a
) Allium acutiflorum, (b
) A. ampeloprasum, (c
) A. atroviolaceum, (d
) A. polyanthum, (e
) A. scorodoprasum subsp. rotundum, (f
) A. scorodoprasum subsp. scorodoprasum, (g
) A. sphaerocephalon, (h
) A. vineale, (i
) A. carinatum, (j
) A. flavum, (k
) A. melanantherum, 

F
i
g
. 
6
. 
Cell pattern of outer bulb tunic (inner surface) of selected Allium species. (a
) Allium paniculatum, (b
) A. stamineum, (c
) A. ursinum, (d
) A. pendulinum, (e
) A. triquetrum, (f
) A. moly, (g
) A. subhirsutum, (h
) A. cepa, (i
) A. fistulosum, (j
) A. sibiricum, (k
) A. schoenoprasum, (l
) A. atropurpureum. Bar = 100 μm. 

F
i
g
. 
7
. 
Cell pattern of outer bulb tunic (inner surface) of selected Allium species. (a
) Allium nigrum, (b
) A. suaveolens, 
(c
) A. saxatile, (d
) A. oreophilum, (e
) A. ochroleucum, (f
) A. albidum, (g
) A. angulosum, (h
) A. flavescens, 
Allium subgenus Butomissa 
Allium ramosum, the only representative of this subgenus examined in this study, is easily distinguished by its characteristic fibrous and reticulate tunics (Fig. 3a) consisting of elongated cells, consis-tent with results from Choi and Oh (2011). 
Allium subgenus Cepa 
A pattern of rectangular to elliptic cells was recorded (Fig. 6h–k). The sculpture was quite distinct and consisted of cells with thick walls, giving the bulb tunic an almost perforated structure (Figs. 3b–e, 6h–k). Calcium oxalate crystals were very common components of such ultrasculpture in this subgenus. The calcium oxalate was crystallized in the form of regular pyramidal prisms (Fig. 6h,i) or such prisms with blunt ends (Fig. 6j). Such crystals correspond respectively to the cepa and schoenoprasum types described by Chartschenko (1932). 
Allium subgenus Melanocrommyum 
No specific pattern was identified for this subgenus. Allium atropurpureum showed striate ultrasculpture with cells remarkably elongated (Figs. 3f, 6l). In contrast, A. nigrum develops a specific network on the bulb tunic surface (Figs. 3g, 7a) and consequently a specific ultrasculpture visible by SEM. Such structure has not been observed previously; Aedo (2013) reported striate ultrasculpture with elongated spindle-shaped cells. 
Allium subgenus Microscordum 
Allium monanthum showed a very distinct her-ringbone pattern of ultrasculpture (Fig. 3h), as also given by Choi and Oh (2011), but such a pattern cannot be regarded as specific to this subgenus. Some North American taxa of subgenus Amerallium (e.g., A. crispum Greene, A. bolanderi 
S. Watson, A. serra McNeal & Ownbey) also have such bulb tunic ultrasculpture (McNeal, 1992; McNeal and Jacobsen, 2002; Nguyen et al., 2008). In this context, note that subgenus Microscordum is most closely related to subgenus Amerallium (Friesen et al., 2006). 
Allium subgenus Polyprason 
The examined taxa did not present distinct ultra-sculpture under SEM. Hexagonal to rectangular cell patterns were recorded (Fig. 7b–d). Allium moscha-tum was characterized by a bulb tunic which breaks into strips (Fig. 4a) and consequently it resembles reticulate ultrasculpture. Allium saxatile had characteristic hexagonal cells with calcium oxalate crystals in the form of fine crystal grains typically deposited by gravity on the bottom wall of the cell (Fig. 7c). This corresponds to the globosum type of calcium oxalate crystals described by Chartschenko (1932). 
Allium subgenus Reticulatobulbosa 
The bulb tunics are fibrous with reticulate ultra-sculpture and a linear arrangement of cells (Fig. 4b–g). An almost similar appearance was described for species of the same section, Reticulatobulbosa: 
A. koreanum H.J.Choi & B.U.Oh and A. splendens Willd. ex Schult.f. (Choi and Oh, 2011). 
Allium subgenus Rhizirideum 
The taxa show characteristic linear ultrasculpture under SEM, following the long axis of the elongated cell walls (Figs. 4h–l, 7e–i). This pattern proved to be specific to this subgenus. Krahulec (1980) found that leaf epidermal anatomy is also uniform in this subgenus. 
CONCLUSION 
The ultrasculpture and cell pattern of the outer bulb tunic are generally differentiated within par-ticular evolutionary lines of Allium. Although those characters do not directly indicate basal or advanced evolutionary levels, variation of ultra-sculpture is sufficient to distinguish species within subgenus Amerallium, and characters of ultra-sculpture or cell shape are diagnostic for some subgenera. The results indicate that Allium bulb tunic ultrasculpture is a useful character for taxonomic delimitation and species determination. It should help in analysis of the relationships between species of the first evolutionary line (Friesen et al., 2006), particularly in representatives of subgenus Amerallium. 
ACKNOWLEDGEMENTS 
I thank Prof. Zbigniew Szeląg (Jagiellonian University, Cracow) for valuable advice and for verifying specimen determinations, and Dr. Olga Woźnicka (Jagiellonian University, Cracow) for tech-nical assistance. 
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