Cambial Variants Combine Successive Cambia and Intraxylary Phloem in Convolvulaceae in Taiwan

Secondary stem growth develops different cambial variants in Convolvulaceae. Here, the cambial variant features of 17 species in seven genera (Convolvulaceae) in Taiwan are presented. The xylem rings produce various successive cambial types and the primary xylem and intraxylary phloem are produced in the outer and inner pith, respectively. The two Argyreia species have round or elliptical stems with continuous secondary xylem and phloem rings. In the eight Ipomoea species, secondary growth has two to four layers of successive cambia and xylem, dispersed with parenchyma tissue, except for I. nil and I. violacea with one layer of successive cambia. The first secondary xylem segments are separated by few or many xylem rays: I. cairica and I. obscura have three to five xylem rays and I. triloba has numerous xylem rays. The first secondary xylem of Erycibe henryi is divided by numerous rays in small stems, but develops more layers, as adjacent segments separated by xylem rays, in larger stems. Owing to continuous vascular bundle division, it has a dissected xylem. The secondary growth of Distimate tuberosa and Operculina turpethum produces two layers of successive cambia;the secondary successive cambium is divided evenly by rays into many arcs/segments. The stem thickness of I. pes-caprae subsp. brasiliensis increases via concentric successive cambia. Owing to shallowly lobed stems with directional successive cambia, I. obscura and I. triloba stems are irregularly shaped. I. littoralis and Stictocardia tilifolia stems are triangular without directional successive cambia. I. hederifolia and Merremia gemella stems have two to three deep lobes. Parenchyma proliferation results in thicker cortex with mucilaginous canals. The xylem vessels are dispersed and diffuse-porous;the vasicentric paratracheal parenchyma around them is common to all species. A bracketed key was developed comparing the secondary xylem structures of the 17 species, providing a basis for further morphological studies.

Comparison of Flavonoid Profiles between Leaves and Stems of <i>Calystegia soldanella</i>and <i>Calystegia japonica</i>

Two species of Calystegia, C. soldanella and C. japonica which both are vine perennials belong to Convolvulaceae habituated in extremely different environment. In order to elucidate the effect of flavonoids to tolerate environmental stress we chose a sand-dune plant C. soldanella, under unfavorable conditions such as nutrients deficiency, strong irradiance, and broad differences of temperature during day and night and compared this plant with C. japonica habituated under mild environment. Several kinds of flavonoids were found in both plants. Especially, quercetin glycosides and kaempferol glycosides were found as major flavonols in both plants. In C. soldanella, kaempferol 3-O-galacto-sidee-7-O-glucoside, kaempferol 3-O-digalactoside-7-O-glucoside, kaempferol 3-O-galactoside-7-O-galactoside and 4’-hydroxyflavone 7-O-glucoside were found. While in C. japonica, quercetin 3-O-galactoside 7-O-glucuronide, quercetin 3,7-O-digalactoside and kaempferol 3-O-galactoside 7-O-glucoside were found. Also, kaempferol glycoside was a major flavonol in C. soldanella, in contrast to quercetin glycoside as major flavonol in C. japonica. The content of total phenolic compounds was similar in two species but the content of total flavonoid compounds was higher by 1.5 times in C. japonica than that of C. soldanella.