生物谷：蘭科植物是植物界種類最為豐富的花卉植物,，但是關(guān)于它的起源問題一直沒有弄清。美國科學(xué)家近日對一個含有蘭花花粉化石的蜜蜂琥珀研究發(fā)現(xiàn),，蘭科植物起源于大約8000萬年前的共同祖先,。8月30日的《自然》雜志以封面文章的形式刊載了這一研究成果。
研究蘭花起源問題相當困難,，因為蘭花的化石非常罕見,，這其中的原因多種多樣。比如,，它們的種子呈粉塵狀,，花粉很容易就溶解在用來提取花粉化石的酸溶液里。另外,，蘭花喜陰,，這使得它們倒地后容易腐爛，很難形成化石,。
這個特殊的蜜蜂琥珀幫助科學(xué)家解決了這一難題,。美國哈佛大學(xué)的Santiago Ramírez和同事通過分析，確認了這只蜜蜂身上所帶的正是蘭花花粉化石,，并根據(jù)這種花粉的結(jié)構(gòu),，將其歸進了斑葉蘭亞族（subtribe Goodyerinae）。與現(xiàn)存的種類比較起來,，這種花粉與在多米尼加發(fā)現(xiàn)的兩種蘭科植物花粉十分相像,。
接下來，研究小組利用現(xiàn)存55個屬的蘭花的遺傳信息建立了一個蘭花進化族譜,，確定了現(xiàn)存蘭花種類之間的親緣關(guān)系,，從而推測它們可能的進化分歧時間。
經(jīng)過測定,，這塊琥珀的年齡為1500萬－2000萬年,。假設(shè)蘭花的進化速率相對穩(wěn)定，那么可以推測蘭科植物的共同祖先大約生長在至少7600萬年前,，也就是白堊紀的晚期,。Ramírez半開玩笑地說道：“恐龍很可能曾從蘭花叢中漫步走過。”
紐約植物園的蘭花專家Kenneth Cameron欣喜地說：“這簡直太美妙了！這正是蘭花學(xué)界期待以久的事情,。”（科學(xué)網(wǎng) 梅進/編譯）
原始出處：
Nature 448, 1042-1045 (30 August 2007) | doi:10.1038/nature06039; Received 17 January 2007; Accepted 21 June 2007
8月30日Nature封面
Dating the origin of the Orchidaceae from a fossil orchid with its pollinator
Santiago R. Ramírez1, Barbara Gravendeel2, Rodrigo B. Singer3, Charles R. Marshall1,4 & Naomi E. Pierce1
Museum of Comparative Zoology, Harvard University, 26 Oxford St., Cambridge, Massachusetts 02138, USA
Nationaal Herbarium Nederland, Universiteit Leiden, P.O. Box 9514, Leiden, The Netherlands
Depto Botânica, Instituto de Biociências, Universidade Federal do Rio Grande do Sul, Av. Bento Gonçalves 9500, RS 91501-970, Porto Alegre, Brasil
Department of Earth and Planetary Sciences, Harvard University, 20 Oxford St., Cambridge, Massachusetts 02138, USA
Correspondence to: Santiago R. Ramírez1 Correspondence and requests for materials should be addressed to S.R.R. (Email: [email protected]).
Since the time of Darwin1, evolutionary biologists have been fascinated by the spectacular adaptations to insect pollination exhibited by orchids. However, despite being the most diverse plant family on Earth2, the Orchidaceae lack a definitive fossil record and thus many aspects of their evolutionary history remain obscure. Here we report an exquisitely preserved orchid pollinarium (of Meliorchis caribea gen. et sp. nov.) attached to the mesoscutellum of an extinct stingless bee, Proplebeia dominicana, recovered from Miocene amber in the Dominican Republic, that is 15–20 million years (Myr) old3. This discovery constitutes both the first unambiguous fossil of Orchidaceae4 and an unprecedented direct fossil observation of a plant–pollinator interaction5, 6. By applying cladistic methods to a morphological character matrix, we resolve the phylogenetic position of M. caribea within the extant subtribe Goodyerinae (subfamily Orchidoideae). We use the ages of other fossil monocots and M. caribea to calibrate a molecular phylogenetic tree of the Orchidaceae. Our results indicate that the most recent common ancestor of extant orchids lived in the Late Cretaceous (76–84 Myr ago), and also suggest that the dramatic radiation of orchids began shortly after the mass extinctions at the K/T boundary. These results further support the hypothesis of an ancient origin for Orchidaceae.
