根据中国麻黄属植物分类及麻黄属起源和演化研究中存在的争论,本论文主要进行了分类学、形态学、微形态学、解剖学、形态发生学、孢粉学、古植物学、植物生态学和植物地理学等方面的研究.
1、分类学
从性状变异式样的分析入手,结合标本馆工作和野外调查,确认了中国麻黄属植物共有13个种；合并了丽江麻黄（Ephedra likiangensis）、雌雄麻黄（E.fedtschenkoae）；澄清了前人在细子麻黄（E.regeliana）、灰麻黄（E.glauca）、草麻黄（E.sinica）和双穗麻黄（E.distachya）等种类鉴定中混乱的问题,并描述了一个新种——日土麻黄（Ephedra rituensis Y.Yang,D.Z.Fu et G.Zhu）.
2、形态学
提供了中国麻黄属种类的标本（包括模式标本）照片资料及中国麻黄属植物的雌球花和雄球花的照片资料,为麻黄属分类和系统学研究提供了证据.
3、微形态学
首次报道了中国麻黄属植物的种子表面微形态特征,聚合囊表面纹饰、小枝表面特征.
种子表面特征可分为4种类型.类型Ⅰ:种子表面平滑,包括:中麻黄（Ephedraintermedia）、双穗麻黄、细子麻黄等；类型Ⅱ:种子表面具疣状突起,仅发现木贼麻黄（E.equisetina）一种；类型Ⅲ:种子表面具横向片层状突起,仅有斑子麻黄（E.rhytidosperma）一种；类型Ⅳ:种子表面具纵条纹,包括喜马拉雅特有的3个大种子的种类,即矮麻黄（E.minuta）、山岭麻黄(E.gerardiana）和藏麻黄(E.saxatilis）.
对小枝表面扫描电镜下的微形态构造的研究并没有发现前人报道的毛状体特征,而只有一些疣状角质突起和有变异的气孔,同时注意到,麻黄属植物的小枝表面特征受到生境、发育阶段的影响.
麻黄属聚合囊顶孔开口处具脑波状纹饰,而聚合囊表面纹饰具二级纹饰.麻黄属聚合囊表面纹饰非常独特,为该属在地层中雄性生殖构造的发现提供了可参考的性状.
4、孢粉学
补充了麻黄属中非常特化的种—斑子麻黄的孢粉资料,同时也对膜果麻黄（Ephedra przewalskii）、中麻黄、细子麻黄和木贼麻黄的孢粉重新进行了研究.结果表明斑子麻黄的花粉形态也非常特殊,其纵肋数目5条左右,纵肋波状扭曲,肋间沟槽内透明线发达且分枝.膜果麻黄的花粉与前人描述的一致,但是,中麻黄、细子麻黄和木贼麻黄的花粉形态可能受到发育的影响而与前人报道中描述的有些差异.讨论了麻黄属4种花粉类型的演化趋势.
5、形态发生学
对麻黄属雌球花三种代表类型的个体发育研究表明,三胚珠球花发育早期球花主轴的顶芽发育,双胚珠球花的顶芽没有发育,而在单胚珠球花中,雌性生殖单位直接占据顶芽的位置发育.这三种类型也代表了麻黄属球花演化的三个阶段,三胚珠球花代表麻黄属雌球花的原始式样,而单胚珠雌球花则为麻黄属雌球花最为特化的式样.总之,麻黄属雌球花有简化的趋势,伴随着这种趋势,雌球花苞片数目减少、种子数目减少、种子体积增大、表面复杂度增加.
6、解剖学
对斑子麻黄种子表面微构造的形态发生及解剖研究表明,斑子麻黄雌性生殖单位发育早期,其表面为平滑型,因此,突起为次生的.这些突起是由雌性生殖单位外盖被表皮细胞的外壁向外突出形成,这种突出生长常常在相邻细胞之间同时发生,因此,出现片层状构造.石蜡切片显示,这些突起在发育早期有完整的细胞核、细胞质等结构,但在种子发育晚期和成熟后,这些外壁突起的细胞成为空腔隙,本文对这种构造的生态学意义进行了分析.
7、古植物学
本文描述了早白垩麻黄科的2个大化石种.
古斑子麻黄（Ephedra archaeorhytidosperma Y.Yang,B.Y.Geng et D.L.Dilcher et Z.D.Chen）发现于辽西义县组尖山沟层,时代为早白垩的芭雷姆期.该种的雌球花具2对苞片、1或2枚种子、珠孔管短直或顶部稍弯、种子表面具横列片层状纹饰等特征而与现存的斑子麻黄特征最为相近.二者之间如此多的相似之处只有一种解释,那就是它们曾经有过共同祖先.因此,该种应归属于麻黄属的肉苞组.古斑子麻黄雌球花特征的稳定性同时也表明,在麻黄属中也存在所谓的“形态演化停滞现象（morphological stasis）”,而这种现象也是首次在买麻藤类植物中报道.
星学异麻黄（Alloephedra xingxueii J.R Tao et Y.Yang）产于吉林大拉子组,时代属早白垩的阿普特期——阿尔布期.该种雌球花具2对苞片、2枚种子,种子长椭圆形且具短的珠孔管与现存麻黄科植物最为相近,但是,其分枝式样与麻黄属不同,因此,本文在麻黄科中建立了一新属新种.此外,麻黄科植物常被看作是干旱区植被的代表,但是,对星学异麻黄当时所处的环境研究发现,大拉子组当时具有较明显的亚热带气候条件下的植被性质,因此,星学异麻黄即使需要干旱的条件,可能也只是局部小生境的条件.
8、生态学和植物地理学
本文首次对麻黄属植物生存环境中的水热条件进行了调查.从所选择的8个分布点来看,除了拉萨外,在麻黄属生殖生长期,其余7个分布点的湿度均是一年中最底的时期,而温度在这个时期逐渐升高.
对各地区内麻黄属种类的分布情况的分析发现,麻黄属的种类主要集中在三个地区,一是我国西北、前苏联的中亚地区及邻近地区,二是美国西南部、墨西哥西北部的地区,三是南美的智利、阿根廷等地.
Abstract
The genus Ephedra L. (Ephedraceae) is one of the three extant genera of the Gnetales. The systematics and evolution of the genus has been one topic of many studies in the past several decades and remain unresolved. The present thesis is a comprehensive study on all species of Ephedra from China based on morphological, anatomical, ontogenetic characters and fossil evidence with a focus on the taxonomy, the evolution of the female cones, and the ecology and distribution patterns of the genus.
1. Taxonomy
Variation patterns of all available characters in Ephedra from China are studied both in the field and in herbarium. Thirteen species are recognized from China, among which, Ephedra rituensis Y. Yang, D. Z. Fu et G. Zhu is described new to science. The traditionally accepted species, E. likiangensis and E. fedtschenkoae are recognized as synonyms of E. saxatilis and E. monosperma respectively. The identities of five traditionally confused species, E. regeliana, E. sinica, E. distachya, E. intermedia and E. glauca are elaborated.
2. Morphology
All Ephedra species from China are illustrated with great details on male and female cones. The photographs provide valuable information of characters including peduncle of cone, bract, and micropylar tube etc. for classification and identification of Ephedra species from China. Ephedra lomatolepis is demonstrated to belong to sect. Pseudobaccatae because the bracts of its female cones are fleshy at maturity.
3. Micromorphology
Seed, synangium, and branchlet surface sculpture of some Ephedra species are studied using SEM and described for the first time, and their systematic significance is discussed.
Four types of seed surface sculpture are described: Type I is smooth (E. intermedia, E. distachya, E. regeliana) , Type Ⅱ possesses warty structures (E. equisetina) , Type Ⅲ bears transverse laminar protuberances (E. rhytidosperma) , and Type Ⅳ is striated (E. gerardiana, E. saxatilis. E. minuta) .
Study on branchlet surface sculpture does not reveal any hair-like structures as recorded by previous authors; only some warty cuticles on the ridges and variable stomata in the grooves are noted.
The surface of synangium in Ephedra has secondary sculpture while the lip of the openings of synangium resembles the cerebral waves. This character is distinct in seed plants and is useful in fossil identification for the Ephedraceae.
4. Palynology
Pollen of Ephedra from China is studied. Four types of pollen have been found in the genus, namely Type A, B, C, and D, according to the number and structure of ridges and structural characters of grooves. The results indicate that E. rhytidosperma bears pollen with 5 waved ridges and developed hyaline lines in the grooves, which is typical for Type A of pollen morphology in the genus. The evolution of pollen of the genus is discussed. It is considered that the evolutionary tendency of pollen morphology in Ephedra is from Type D to Type A.
5. Ontogeny
Three types of female cones of Ephedra are recognized according to the number of seeds per cone, namely uni-ovulate cone, bi-ovulate cone, and tri-ovulate cone. It is suggested that terminal bud of primary cone axe is developed in tri-ovulate cone and disappears in bi-ovulate cone. In the most extreme condition in uni-ovulate cone, the female reproductive unit (FRU) occupies the position of the terminal bud. An evolutionary trend of reduction is supported in the genus from tri-ovulate to uni-ovulate cone, in which the bract number and seed number are reduced, and the seed size and seed surface sculpture are increasing.
6. Anatomy
Ephedra rhytidosperma is studied in detail. The FRU surface is smooth in its early developmental phases, while the laminar structure is secondary. The secondary sculpture is formed by the outgrowth of the outer tangential wall of the epidermal cell, and this kind of protuberance always occurs in the adjoining cells, which makes the laminar protuberances. The transverse and longitudinal section of the developing ovulate structure and the mature seed show that the projecting epidermal cells usually have nuclear and other cytoplastic structures in the early developmental stages, empty when mature.
7. Palaeobotany
One genus and two megafossil species, Alloephedra xingxueii J. R. Tao et Y. Yang and Ephedra archaeorhytidosperma Y. Yang, B. Y. Geng, D. L. Dilcher et Z. D. Chen, are described as new to science.
Ephedra archaeorhytidosperma is from the Jianshangou Bed, Yixian Formation, Shangyuan District, Beipiao City of western Liaoning Province, Northeast China. This species contains many morphological and anatomical characters comparable to the living Ephedra and E. rhytidosperma in particular, suggesting a common ancestor.
The similarity of reproductive organs between the fossil and extant species also demonstrates that morphological stasis might have occurred in Gnetales.
Alloephedra xingxueii J. R. Tao et Y. Yang is from Dalazi Formation, Jilin Province, China. The reproductive characters are similar to those of the living Ephedra while the vegetative organs are characteristic of alternate leaves and branching patterns; as a result, the fossils are attributed to a separate genus and species. The species might have occupied an arid microhabitat because Ephedraceae is an important indicator for an arid climate, and the prevailing climate of Dalazi Formation in Early Cretaceous is warm and humid.
8. Ecology and Phytogeography
The water and temperature condition in the distribution area of some Ephedra species is studied for the first time. It is suggested that Ephedra species usually experience a very dry condition while a rising temperature in the reproductive period.
The extant Ephedra has three distribution centers: Tajikistan and its adjacent areas, Southwest US and the Northwest Mexico, and the adjacent areas of Chile and Argentina in South America.
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