【摘要】 蚬木Excentrodendronhsienmu雌雄花在发育早期均有小孢子和大孢子的早期发育,难以区分。蚬木子房5室,具中轴胎座,每室2胚珠;胚珠倒生,厚珠心,双珠被,成熟胚囊内珠被3层细胞,外珠被3–4层细胞,内外珠被共同形成之字形珠孔;单细胞孢原,大孢子四分体主要为线形,稀为T形,通常合点端大孢子为功能大孢子,胚囊为蓼型;在大孢子发生和胚囊发育时期有退化现象,成熟胚囊时期退化率和种子退化率分别达88%和91%。蚬木属Excentrodendron在内外珠被层数上与柄翅果属Burretiodendron明显不同,也与翅子树属Pterospermum、非洲芙蓉族Dombeyeae不同。蚬木属与柄翅果属的分离一直没有得到广泛接受,但胚胎学证据支持蚬木属的建立;与广义锦葵科Malvaceaes.l.其他属胚胎学资料的比较表明,蚬木属在广义锦葵科中较孤立。更多还原

【Abstract】 Segregation of Excentrodendron and Burretiodendron has hardly been accepted despite their distinct pollen morphology. Megasporogenesis and embryo sac development were studied in Excentrodendron hsienmu in order to examine the basis of segregation of Excentrodendron and Burretiodendron and to study the affinity of Excentrodendron. Excentrodendron hsienmu is dioecious and a large number of flower buds developed every year on mature male and female trees but flower blossoming and fruiting did not occur every year and there was a cycle of 3–4 years. Staminate and pistillate flowers were not distinguishable in the early development stages since both microsporogenesis and megasporogenesis were observed in staminate and pistillate flowers, respectively. Megasporogenesis in staminate flowers degenerated after demarcation of megaspore mother cell or rarely after megaspore tetrads. The monosexual flowers of Excentrodendron were probably derived from bisexual flowers. The ovule was anatropous, bitegmic, and crassinucellate. The primary archesporium of ovules consisted of usually one cell and integument initials were not demarcated at the time of the differentiation of the archesporium. The outer and inner integument of the mature embryo sac was 3–4 and 3 cells thick, respectively. The megaspore mother cell was usually deeply seated in the nucellus before meiosis and gave rise to a linear or rarely T-shaped tetrad. The development of embryo sac conforms to the Polygonum Type. Degeneration was observed commonly after demarcation of megaspore mother cells; 88% of embryo sacs degenerated and only 9% of ovules developed to seeds. Excentrodendron shares with Burretiodendron a number of plesiomorphic characters that are commonly found in members of Malvales. It differs from Burretiodendron mainly in the thickness of the inner integument which is 3 cells thick in Excentrodendron but 4–5 in Burretiodendron. In addition, archesporium is usually unicelled in Excentrodendron but multicelled in Burretiodendron. Segregation of Excentrodendron is therefore supported by the present study. Embryologically, Excentrodendron differs also from Pterospermum, Dombeyeae, and other taxa of the expanded Malvaceae, mainly in the thickness of integuments and number of archesporial cells. The present study does not support the placement of Excentrodendron in the tribe Dombeyeae of Malvaceae s.l.更多还原