Cryptic Dioecy of Symplocos Wikstroemiifolia Hayata(Symplocaceae) in Taiwan

台灣產蕘花葉灰木之隱性雌雄異株之研究

王有禎(Yu-Chen Wang) ； 胡哲明Jer-Ming Hu

《Botanical Studies》 52卷4期 (2011/10) Pp. 479-491

摘要

蕘花葉灰木 (Symplocos wikstroemiifolia Hayata) 是灰木科 (Symplocaceae) 中少數外觀形態為雄花/ 兩性異株花 (androdioecy) 的物種。雖然過往的研究指出蕘花葉灰木可能是隱性雌雄異株 (cryptic dioecy)，但是對該物種在野外生育地的性別表現狀況並不清楚。我們針對台灣產的蕘花葉灰木進行生殖系統(breeding system) 與繁殖生物學 (reproductive biology) 的研究。生殖系統的調查結果顯示，來自外觀兩性花上的雄蕊並不具花粉，因此這種型態的花朵應被視為雌花。幾乎所有的開花植株在調查期間只開雄花或雌花，族群中雖然記錄到較多的雄株，但是性別比例並沒有明顯偏離1:1。這些結果符合預想中隱性雌雄異株的特徵。然而，有兩株個體產生了一些可能具有兩性生殖功能的花朵，這顯示少數植株在性別表現上仍具備可塑性。花部外形測量顯示雄花平均具有約12 枚雄蕊但雌花只具有5 枚假雄蕊。每朵雄花並不具有腔室或胚珠，而每朵雌花其子房具有兩室，而每室中具有4 枚胚珠，且胚珠依照大小可以分成兩型。雄株會產生不分支的聚繖花序 (cymes) 與密錐花序 (thyrses)，而雌株只會產生不分支的聚繖花序。以上這些外形特徵有些與過往文獻中的敘述並不一致。開花物候觀察顯示大部分的雄花和雌花在凌晨開放花苞，且單花壽命大約是一至兩天，然而，雄蕊只在乾燥的環境下開裂，因此開裂的時間並不固定。族群中的天然結實率為6.7%，比起其他灰木屬或是雌雄異株的物種，蕘花葉灰木具有較低的天然結實率。總而言之，蕘花葉灰木的性別表現幾乎完全分化為雄性與雌性兩種型態 (gender dimorphism)，但是還是有一些小變異存在於族群中，因此這個物種應被視為隱性雌雄異株。

關鍵字

雄花／兩性異株花 ； 生殖系統 ； 隱性雌雄異株 ； 性別表現分化 ； 生殖生物學 ； 蕘花葉灰木

並列摘要

Symplocos wikstroemiifolia Hayata is one of the few morphologically androdioecious species in Symplocaceae. Although this species has been proposed as cryptically dioecious, little is known about its patterns of sexual expression in the field. We studied the breeding system and reproductive biology of S.wikstroemiifolia in Taiwan. Field investigations showed that anthers of most morphologically hermaphroditic flowers did not produce pollen grains; thus, this flower type should be considered female. Nearly all flowering individuals produced only male or female flowers. The sex ratios were slightly male-biased, but did not significantly deviate from 1:1, congruent with the proposed cryptic dioecy status. However, two individuals produced flowers that may have been functionally hermaphroditic, suggesting a variation of sexual expression in S. wikstroemiifolia. There were about 12 stamens per male flower but only five staminodes per female flower. No locules and ovules existed in the male flowers, while two locules within the ovary of the female flowers contained four ovules each (two large, two small). Male individuals produced cymes and thyrses, whereas female individuals only produced cymes. Some of these morphological characteristics differed from those previouslydescribed. Anthesis of most male and female flowers began before dawn and lasted for one to two days. Nevertheless, anther dehiscence, which only occurred under dry conditions, was not restricted to a specific timeperiod during the day. The mean natural fruit set was 6.7%, which is relatively low compared to those in other Symplocos or dioecious species. In conclusion, S. wikstroemiifolia exhibited a nearly complete gender dimorphism, but with certain flexibility in sexual expression, and should thus be considered cryptically dioecious.

並列關鍵字

Androdioecious ； Breeding system ； Cryptic dioecy ； Gender dimorphism ； Reproductive biology ； Symplocos wikstroemiifolia