晚花澤蘭之不孕花粉外壁的不完全發育

Incomplete Exine Development in Aborted Pollen of Eupatorium serotinum Michx. (Compositae: Eupatorieae)

晚花澤蘭（菊科：澤蘭族）成熟花葯中含有完整花粉及不同發育階段中之不孕小孢子。最末發育小孢子之外壁（比如最幼時期）具10nm直徑之棒紋，不具刺紋。主要為不具蓋層。較成熟花葯中花粉具不連續蓋層下，含有許多分離之圓柱層及為頂狀突起之圓柱刺紋。最成熟花葯中之發育不全小孢子，其蓋層變異大。一般而言，主要者為連續圓柱紋兼增大直徑之刺紋，且其頂部全屬圓形。這些階段之特殊特徵係刺紋基部之間隙。間隙基部為開放，且填滿形似圓柱紋及蓋層。此類結果提供小孢子外壁保留發育早期中發育不全特徵於成熟花葯之直接證據。假使成熟花葯亦含花育成熟外壁之成熟花粉（本種之典型特徵）時，未發育外壁在此花葯中提供早期發育之訊息。未發育外壁獲自沉積岩內之花葯，可提供他法難獲得之個體發展史訊息。

Mature anthers of Eupatorium serotinum Michx. (Compositae: Eupatorieae) have fully formed pollen grains along with microspores that apparently aborted during several stages in development. The latter are enclosed by acetolysis-resistant sacs. The least developed microspore exine (presumably the youngest stage) consisted of rods about 100 nm in diameter, without spines and mainly without a tectum. A more advanced stage had a discontinuous tectum with many unattached columellae and with cylindrical spines having a flat or slightly convex summit. In the most advanced aborted microspores the tectum was variable but mostly continuous and the spines were greatly increased in diameter and all had rounded distal ends. The special feature of these stages was the gaps in the basal portions of the forming spines. The gaps were open basally and filled with structure of the same appearance as columellae and tectum. These results contribute to direct evidence that microspore exines that had aborted early in their development retain the features in mature anthers of that stage(s) of exine development at the time of their abortion. Providing that the mature anthers also contain mature pollen with fully developed exines (typical of the taxon), then the underdeveloped exines within such anthers can provide information about early development. Underdeveloped exines such as those recovered in intact anthers in sedimentary rocks, may provide information about ontogeny that otherwise would be unobtainable.