木兰藤科系统位置评述

木兰藤科(Austrobaileyaceae)含1属2种,是系统学上最孤立的科之一。其花粉类似于最古老的被子植物化石之一:晚白垩世的棒纹粉。最新的分子系统发育研究结果表明,木兰藤科是现存被子植物的基部类群之一,其对于被子植物的起源与早期进化的研究具有重要价值。被子植物(有花植物)的起源和辐射一直是植物学家关注的热点。有关木兰藤科的系统位置一直存在争议。本文对该科系统位置的研究历史与现状进行评述。     

A Scanning Electron Microscopy Survey of Some Maydeae Pollen

Scanning electron microscopy was used to examine the wall sculpturing of pollen from Zea mays L. ssp. mays (maize), Zea mays ssp. mexicana (Schrad.) Iltis (teosinte), Zea perennis (Hitchc.) Reeves and Mangelsdorf (perennial teosinte), and two species of Tripsacum L. The Zea taxa are shown to possess similar pollen types, with spinules scattered regularly over the exine surface. Tripsacum exhibits a distinctly reticuloid pattern, with spinules clumped into isolated lacunae. Hybrids between Zea and Tripsacum are either intermediate in exine pattern or similar to Tripsacum, depending on the genome combination.     

The exine ultrastructure of pollen grains in Gnetum (Gnetaceae) from China and its bearing on the relationship with the ANITA Group

Pollen grains of six species of Gnetum , G. parvifolium , G. hainanense , G. luofuense , G. pendulum , G. cleistostachyum and G. montanum , collected from China were examined using light, scanning and transmission electron microscopy. Pollen grains of Gnetum are subspheroidal or irregular-apolar, inaperturate, 11.21–22.44 µm in long axis and 9.34–20.47 µm in short axis. The exine surface is covered with spinules, 0.50(0.30–0.71) µm long spaced on average 1.12(0.81–1.46) µm apart. The exine is about 0.55 µm thick and comprises ectexine and endexine. The ectexine includes a thin tectum and an infratectal granular layer. The tectum protrudes outwards, forming the spinules. The endexine is composed of discontinuous lamellae, with lacunae between lamellae. The pollen grains of Gnetum are compared with those of Ephedra and Welwitschia , and also those of the ANITA Group of angiosperms, including Amborellaceae, Nymphaeales, Illiciales, Trimeniaceae and Austrobaileyaceae. The exine ultrastructures of Gnetum , Ephedra and Welwitschia are quite similar, consisting of tectum, granular layer and lamellated endexine. The exine ultrastructure of Gnetum is also similar to that of Nymphaea colorata (Nymphaeaceae) in the transitional region between the proximal and distal poles, but differs from that of Amborellaceae, Illicium religiosum (Illiciaceae), Schisandra (Schisandraceae), Trimeniaceae and Austrobaileyaceae. This comparison of exine ultrastructure provides new evidence for consideration of the relationship between Gnetum and the ANITA Group.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 146 , 415–425.     

Development and structure of the female gametophyte in <Emphasis Type="Italic">Austrobaileya scandens</Emphasis> (Austrobaileyaceae)

Austrobaileyales, comprising the four families Austrobaileyaceae, Trimeniaceae, Schisandraceae, and Illiciaceae, are included in the basal angiosperms along with Amborellaceae and Nymphaeaceae. Here, we present the first developmental study of the female gametophyte in Austrobaileya scandens, the only species of Austrobaileyaceae, which are sister to the rest of the Austrobaileyales. Austrobaileya scandens has a four-celled/four-nucleate embryo sac as in the derived families of the order, e.g., Illiciaceae and Schisandraceae. It is monosporic, with the chalazal megaspore of a tetrad developing into the embryo sac composed of an egg cell, two synergids, and one polar nucleus. This mode of embryo sac formation was first reported in Schisandra over 40 years ago and should now be established as the Schisandra type. Its occurrence in A. scandens shows that the Schisandra-type embryo sac is likely common to the whole Austrobaileyales as well as to Nymphaeaceae. Amborellaceae were recently reported to have an eight-celled/nine-nucleate embryo sac, clarifying that none of the basal angiosperms has the seven-celled/eight-nucleate Polygonum-type embryo sac found in the majority of angiosperms, and that the Polygonum-type embryo sac represents a derived character state in angiosperms.     

DNA C-values in seven families fill phylogenetic gaps in the basal angiosperms

The evolutionary significance of the c . 1000-fold range of DNA C-values in angiosperms (1C =  c . 0.1–127.4 pg) has often attracted interest. A recent analysis, which superimposed available C-value data onto the angiosperm phylogeny, that placed Ceratophyllaceae as the most basal angiosperm family led to the conclusion that ancestral angiosperms were characterized by small genomes (defined as 1C £ 3.5 pg). However, with the recent increase in DNA sequence data and large-scale phylogenetic analyses, strong support is now provided for Amborellaceae and/or Nymphaeaceae as the most basal angiosperm families, followed by Austrobaileyales (comprising Schisandraceae, Trimeniaceae and Austrobaileyaceae). Together these five families comprise the ANITA grade. The remaining basal angiosperm families (Ceratophyllaceae, Chloranthaceae and magnoliids), together with monocotyledons and eudicotyledons, form a strongly supported clade. A survey showed that C-value data were scarce in the basal angiosperm families, especially the ANITA grade. The present paper addresses these phylogenetic gaps by providing C-value estimates for each family in ANITA, together with C-values for species in Chloranthaceae, Ceratophyllaceae and a previously unrepresented family in the magnoliids, the Winteraceae.  © The Linnean Society of London, Botanical Journal of the Linnean Society , 2002, 140 , 175–179.