ISSN 0096-3925, Moscow University Biological Sciences Bulletin, 2010, Vol. 65, No. 3, pp. 98–103. © Allerton Press, Inc., 2010. Original Russian Text © A.A. Sinyushin, 2010, published in Vestnik Moskovskogo Universiteta. Biologiya, 2010, No. 3, pp. 11–16. 98 INTRODUCTION The investigation of developmental abnormalities, teratology, has recently obtained a somewhat different meaning as compared with a period of its origin. Except function of direct description of certain terato- logical phenomena, this part of morphology entered a field of modeling of developmental processes, muta- tion analysis, and even evolutionary reconstructions in light of the Evo-Devo concept. Teratology itself has tightly associated with contemporary molecular devel- opmental genetics, the latter significantly pushing out the structural approach in understanding of morpho- logical abnormalities. Fasciation represents one of the most widespread anomalies of plant development. One may propose that the main problem in discussion of this phenome- non is absence of satisfactory definition. Numerous authors give similar and, at the same time, different characteristics [1, 2]. Studies of model objects, mainly Arabidopsis thaliana (L.) Heynh. (Brassicaceae), give a certain key towards understanding this problem. Genetic control of formation and specialization of stem apical mer- istem (SAM) is studied precisely enough. It had been demonstrated that basic mechanism of regulation of SAM activity is negative feedback between gene WUS- CHEL (WUS) and multiple negative regulators of its expression (CLAVATA (CLV), FASCIATA (FAS) etc.) [3]. Mutations in these genes lead to overexpression of WUS in SAM and floral meristem (FM); as a result, abnormal enlargement of this meristem occurs, namely fasciation. However, investigations on varia- tions on fasciation in different taxa clearly demon- strate how many different transformations the basic model (designed for model object with simple inflo- rescence and actinomorphic flower) can undergo. Many plants are known to possess inherited forms of fasciation affecting SAM only and not FM. Works in which structure of abnormal organs could be analyzed from the positions of molecular developmental genet- ics are obviously lacking. The most detailed review devoted to fasciation is still the work of O.E. White [1]. The structural approach seems very important when combined not only with modern molecular systemat- ics [4], but also with contemporary developmental genetics. The flower, an organ with discrete structure com- posed of parts with more or less constant number and position, represents a convenient model for studies on mechanisms of fasciation. The given work is aimed at generalization of material dealing with flower fascia- tion, estimation of mechanisms underlying it and for- mulation of more or less comprehensive definition of the given phenomenon. MATERIALS AND METHODS The living or fixed in 70% ethanol material was used for investigations on flower morphology. Flowers and inflorescences of pea line “Lupinoid” were col- lected in 2005–2007 from plants grown on a territory of Zvenigorod Biological Station of Moscow State University (Odintsovo raion, Moscow region). Flow- ers of Allium nutans L., A. cepa L., and Lupinus poly- phyllus Lindl. were collected in 2006–2007 in Ruza raion of Moscow region as components of cultural flora. Fruits of Alisma plantago-aquatica L. were col- lected in 2005 on a territory of “Zhuravlinaya rodina” natural preserve (Taldom raion, Moscow region). Flowers of Syringa vulgaris L. (wild lilac and cv. Paul Hariot) were collected in 2007 in the Botanical Gar- den of Moscow State University. The material fixed in ethanol was prepared for scanning electron micros- copy (SEM) according to protocol described in work Flower Fasciation: I. Origin of Enlarged Meristem A. A. Sinyushin Genetics Department, Moscow State University, Moscow, Russia e-mail: sinjushin@pisumsativum.org Received May 5, 2009 Abstract—Different ways of formation of fasciated floral meristem were analyzed. It has been demonstrated that distinguishing between phenomena of enlargement of a single growing point and fusion of a few into sin- gle one is impossible. The frequency of abnormalities is proposed as criterion for such classification. Key words: flower, fasciation, floral meristem DOI: 10.3103/S009639251003003X