地质时期樟科植物花化石及其系统演化意义
摘 要: 该研究对地质时期樟科植物花化石的主要类群,即Androglandula、Lauranthus、Mauldinia、Neusenia、Perseanthus和Potomacanthus属分别从属和种的形态特征、分布、地层以及系统意义进行了论述,并结合现代樟科植物从地层和分布、花序类型、花部形态特征和显微构造特征进行了分析。结果表明:(1)樟科植物在中晚白垩纪期,已经起源于劳亚古陆的中纬度区域。(2)樟科植物的花序类型为Mauldinia属的侧生花序类型和假伞形花序类型。(3)花为3基数的两性花,花被片6枚排列为2轮,雄蕊12或6,排列为4、3或2轮,最内轮雄蕊不育,第三轮雄蕊基部常见一对附属腺体,雄蕊药室瓣裂,4或2药室,雌蕊为单心皮。(4)花被片上常有大量的油细胞、并列型气孔器和单细胞毛。该研究结果中樟科花化石的发现,为樟科植物的系统演化提供了古生物学的证据和资料。
关键词: 樟科, 花化石, 地质时期, 系统演化
中图分类号: Q941
文献标识码: A
文章编号: 1000-3142(2018)02-0210-10
Flower fossils of Lauraceae in the geological time and its phylogenetic evolutionary significance
HUANG Honghui, LI Jingzhao*
( School of Life Sciences and Technology, Nanyang Normal University, Nanyang 473061, Henan, China )
Abstract: This article systematically reviews the fossil record of the Lauraceae flower, including Androglandula, Lauranthus, Mauldinia, Neusenia, Perseanthus and Potomacanthus which were found in the geological times, the morphological characters, distribution, stratum and phylogenetic significance of these genera and species are systematically discussed. This article explores the stratum, distribution, inflorescence types, floral morphological characters, microstructural characters with the modern Lauraceae. The results were as follows: (1) Lauraceae originated in the mid-latitude region of the Laurasia from middle to late Cretaceous. (2) Two inflorescences are found in the fossil flower of Lauraceae, one is Mauldinia type, which has elongated axes bearing distinctive, spirally arranged lateral, bilobed cladode-like units with five sessile bisexual flowers on the adaxial surface, the other is pseudoumbel type which has three sessile and closely spaced flowers with enclosed by two broad and strongly truncate bracets.(3) Bisexual flowers with three cardinal numbers, six perianth lobs arranging in two whorls, twelve or six stamens in four, three or two whorls, innermost whorl reduced to staminodes, the third whorl stamen usually bearing two sessile and distinct basal glandular protuberances, anthers have two or four valved chamber, the gynoecium has single carpel. (4) A large number of oil cells, paracytic stomatal apparatus and unicellular hairs are often present on perianth. The flower fossils of Lauraceae provide geological and historical evidences for the phylogenetic evolutionary study of the Lauraceae.
Key words: Lauraceae, flower fossils, geological time, phylogenetic evolution
樟科是一個包含约50属、2 500~3 000种的木本植物类群[除草本植物无根藤属(Cassytha)外],此类群的现代种类广泛分布于世界的热带和亚热带地区,以亚洲东南部和中、南美洲为现代分布中心,尤以巴西的属和种最多,亦产于非洲和大洋洲,欧洲仅在地中海和高加索等地区分布有月桂属(Lauraus)的植物(李锡文等,1982)。然而,地质时期的樟科植物广布于世界各大陆,特别是欧亚和北美的化石种类比较多(刀克群等,2011;刘裕生,1990; Bandulska,1926,1929;Balthazar et al,2007;Drinnan et al,1990;Eklund & Kavacek,1998;Eklund,2000;Frumin et al,2004;Herendeen et al,1994,1999;Hill,1986;Pole,2007;Li et al,2009;Takahashi et al,1999,2001;Taylor,1988;Viehofen et al,2008);而保存下来的樟科植物化石主要是木化石、叶化石、花化石和很少的原位花粉,种类最多的属木化石和叶化石。但是,樟科植物木材解剖特征和叶外部形态角质层的研究缺乏该科所特有的形态学识别特征,因此相对樟科植物花化石,其木化石和叶化石就不是那么可靠。现代樟科植物的分类系统主要是基于樟科植物的花序形态(主要为假伞形花序和圆锥花序的对立)、花部形态学特征(花基数、药室数目、苞片脱落否、花被片宿存或脱落)和果实形态(子房位于花被片下的厚壳桂属)而建立的族级或属级的系统演化关系,另外樟科植物花粉因其花粉壁比较薄很难在长期的地质条件下保存,因此樟科植物花化石的发现就显得弥足珍贵,能为我们准确系统了解樟科植物起源和演化提供直接证据,也便于更好地理解现代樟科植物各类群之间的亲缘关系。
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