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Trochodendraceae is the only family of flowering plants in the order Trochodendrales. It comprises two living genera with two species found in south east Asia. The two living species both have secondary xylem without vessel elements, which is quite rare in angiosperms. As the vessel-free wood suggests primitiveness, these two species have attracted much taxonomic attention. == Description == * Deciduous or evergreen trees, up to 20-30 m, sometimes with umbrella-shaped branches (''Trochodendron''). Covering hair, scales etc. absent. * Leaves in spirals at the end of the branches (umbrella-like appearance, ''Trochodendron'') or separate (''Tetracentron''), simple, serrulate or crenulate, with clorantoid teeth, palmately or pinnately divided, brochidodromous or actinodromous, ovate or obovate, with a cordate to cuneate base and acuminate apex, stalked, with thin stipules fused with the petiole (''Tetracentron'') or absent (''Trochodendron''). Idioblasts present, large, branched, sclerenchymatous in ''Trochodendron'' and secretory in ''Tetracentron''. Stomata laterocytic or cyclocytic, hypostomatic. * Stems without xylematic vessels, with tracheids, heterogeneous xylem, uni- and multi-seriate, branches clearly differentiated in unifoliate brachyblasts and macroblasts with distichous phyllotaxis (''Tetracentron''), with nodes (1-)3(-multi)-lacunar, with (1)3(-7) leaf stems. * Hermaphroditic or androdioecious plants. * Terminal Inflorescence in erect, aggregated racemiforms (botryoid or small panicles) (''Trochodendron'') or defined, axillary, multi-floral amentoid spikes with the flower in whorls of 4 (''Tetracentron''). Bracts and bracteoles present or absent. * Perfect flowers, actinomorphic or dissymmetric, yellowish. Short, sub-conical, or hollow receptacle. Hypogynous disk absent. Reduced, very thin perianth, of 4 tepals in 2 decussate whorls (''Tetracentron''), or at most in a recognizable preantheric state (''Trochodendron''). Androecium of 4 decussate stamens in pairs of 40-70 in a spiral, non-versatile, basifixed, tetrasporangial, latrorso, apiculate anthers, dehiscence along 2 longitudinal valves in the theca. Gynoecium superior (''Tetracentron'') to slightly semi-inferior (''Trochodendron''), of 4-11(-17) carpels, syncarpous (alternating with the stamens in ''Tetracentron'') to semicarpous, the dorsal part of the ovary expanded horizontally in the anthesis, abaxially nectariferous, with sunken stomata, free styles (stylodious), dry, papillose, decurrent ventral stigmas, 5-30 anatropous, apotropous, bitegmicous, crassinucelate, pendulous ovules per carpel, placentation marginal in 2 series or apicoaxial. * Fruit in ventricidal or slightly loculicidal capsule or an aggregate of dorsally and ventrally dehiscent semicarpical follicles, with basal and external styles. * Small, flattened, tapered seeds, 3-4 mm in length, with lateral, apical, chalazal wings, with thin testa, with abundant, oily and proteinaceous endosperm, small embryo, with 2 cotyledons. * Pollen in small, granular, spheroidal, tricolpate, tectated-columelliform monads (10-20 μm in diameter), the surface with interwoven bars parallel to the edges of the colpus, which are granular. * Chromosomal number: ''2n'' = 48 in ''Tetracentron'' and ''2n'' = 38, 40 in ''Trochodendron''. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Trochodendraceae」の詳細全文を読む スポンサード リンク
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