| Morphological and quantitative characteristics of leaf structure in 13 Tilia species, floral bract structure of 6 Tilia species, sepals and petals of 3 Tilia species, as well as leaf structure in 3 Grewia species, sepals and petals of 2 Grewia species were observed by means of light microscopy and scanning electron microscopy. The significance in phylogeny and ecological adaptation was discussed. Landscape application of Tilia species studied was evaluated. Main results are as follows:(1)Tilia species studied were characterised by (a) filament or striped wax decoration in leaf surface, (b) only one type of inner margin of outer stomatal rim, either sinuolate or smooth, (c) pith sheath in cross section of leaf stalks. While Grewia species studied didn't have filament or striped wax decoration, had both sinuolate and smooth inner margin of outer stomatal rim in every species, and didn't have pith sheath in cross section of leaf stalks. Therefore, the above three different features can delimit Tilia and Grewia.(2)Presence or absence of leaf epidermis hair and the distribution type, lower leaf epidermis cell shape were different among species of Tilia.a. Epidermis hairs were distributed on upper and lowe leaf epidermis in T. mandshurjca, Grewia biliba var.parviflora, T. platyphyllos var. vitifolia.There are three different types:simple hair,2-4 branched hair,stellate hair. T. platyphyllos var. vitifolia had three types of hairs. Trichome base existed on lower leaf epidermis in T. miqueliana.So characteristics of epidermis hair can be used to identify some Tilia species from each other.b. Lower leaf epidermis cell shape in 3 species of Sec.Tilia(T. henryana,T. mongolica,T. miqueliana) was polygon, anticlinal wall was straight or arched. In the other 10 species of Sec.Tilia, Lower leaf epidermis cell shape was irregular-shaped. Anticlia wall pattern was wavy. Whether cell shape in lower leaf epidermis had phylogenetic significance need further study.(3)The cross-section of leaf midrib and stalks in 13 Tilia species was almost round and oval, Shape of the adaxial surface of stalk, distribution of the epidermis trichome, vascular shape of leaf midribs were different among different species. T. mandshurjca, T. nobilis,T. japonica, T. henryana, T.moltkei, T. miqueliana and T. platyphyllos var. vitifolia were U-shaped in vascular shape of leaf midrib,and the other species were round. T. euchlora and T. american were hollow in leaf stalks cross-section, the others were flush or subflush.(4)Greater similarity was found between upper and lower surface of floral bracts in 6 Tilia species. Floral bracts were polygon or irregular in cell shape of upper and lower surface. The bract surface was covered with waxy coat or cuticles and had types of epidermis hairs, which is similar to leaf surface. However, The cross-section of stalk of floral bracts which is U-shaped or subcolocal in shape is different from that of leaf stalk.(5)Perianth cells have Wrinkle-like or worm-like ornamentation. It is advanced traits in the perianth evolution.(6)Some leaf quantitative characteristics were selected to study the drought resistance of Tilia species by statistical analysis of DPS (Group average method) software (UPGMA), and the results indicated that some species such as T. miqueliana, T. platyphyllos var. vitifolia and Grewia biliba var.parviflora were more drought-torlerant, while T. nobilis and T. moltkei were less drought-torlerant.(7)Leaf anatomical structure showed the developed palisade tissue, dense epidermal hair and waxy coat or cuticles functuioned as drought torlerant and cold hardy structures. Arrangement of spongy tissue in T. henryana, T. americana and T. tomentosa were tighter than the others species, which can infer that T. henryana, T. americana and T. tomentosa were more drought tolerant. However this should be studied further in that the results from leaf morphological features were not consistent with those of cluster analysis of drought resistance in Tilia.(8)Most vestures on vessel walls and helical thickenings in 13 Tilia species, are dot-shaped or conical vestures, occasionally forked or rod-shaped vestures. Dot-shaped vestures occasionally occur on fiber walls of Tilia species. Occasionally small to vestigial vestures are present in fiber pit apertures of T. miqueliana and T. mandshurica. Vestured pits are presumedly present and show high homogeneity in all Tilia species since they are considered as a conservative character and due to ecophylogeny analysis. vestured pits are supposed to show heterogeneity among genera of Tiliaceae according to our observations combined with former research results.(9)Tilia species are beautiful landscape plants. We should combine the morphological features with growth habits in landscape use considering effective application. |
