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Basic Features of Gymnosperm Systematics and Phylogeny as Evidenced by the Fossil Record

Sergei V. Meyen
Botanical Review
Vol. 50, No. 1, Basic Features of Gymnosperm Systematics and Phylogeny as Evidenced by the Fossil Record (Jan. - Mar., 1984), pp. 1-111
Published by: Springer on behalf of New York Botanical Garden Press
Stable URL: http://www.jstor.org/stable/4354028
Page Count: 113
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Basic Features of Gymnosperm Systematics and Phylogeny as Evidenced by the Fossil Record
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Abstract

This paper introduces an integrated system of morphological concepts for gymnosperm fructifications, which does not lean upon any system existing for other higher plants. Comparative analytical treatment of all available characters of the most thoroughly studied fossil genera provided the foundation for an ordered ranking of congregations, each unit being assigned to the status of families, orders and classes. The transformation of the generative and vegetative organs has been traced along various phylogenetic branches. A new large phylogenetic branch (class Ginkgoopsida), beginning with the Lower Carboniferous Calamopityales, has been established. The lineage evolved from this order to Callistophytales and further to Peltaspermales. The family Peltaspermaceae encompasses, among others, plant types formerly regarded as ginkgoaleans. The orders Ginkgoales, Leptostrobales (Czekanowskiales) and Caytoniales evolved from the Peltaspermales. The order Arberiales (glossopterids) evidently evolved from the Calamopityales. In the lineage from Calamopityales to Ginkgoales a common seed type is conserved (platyspermic, non-cupular with two vascular bundles in the integument). Radiospermic seeds are conserved in the class Cycadopsida. In the lineage from Lagenostomales to Trigonocarpales the radially symmetrical cupule underwent modification into an integument of the same type of symmetry. The earliest Lagenostomales with the bilaterally symmetrical cupule evolved into the Cordaitanthales, where the cupule, also undergoing modification, was transformed into a bilaterally-symmetrical integument. In Cordaitanthales and their descendents the Pinales the seeds became secondarily platyspermic (in contrast to the primary non-cupular and primary platyspermic seeds in Ginkgoopsida); their vascularization was progressively reduced. These two orders are grouped into the class Pinopsida. It is believed that angiosperm seeds are in effect radiospermic with a radial cupule, their vascularization also being progressively reduced. If this holds true, the angiosperm ancestry should be sought in the class Cycadopsida. The Caytoniales, Arberiales, Peltaspermales, Leptostrobales and other orders of the class Ginkgoopsida should be excluded from the stock of probable angiosperm ancestors. A new gymnosperm phylogeny has been proposed and the evolution of the phylogenetic branches outlined in terms of the phytochoria system of the geological past. The basic evolutionary innovations took place within the Equatorial Belt and adjacent ecotone areas. Three types of processes, often underrated, have a paramount role in gymnosperm phylogeny. They are defined as follows: (1) homoeotic transformations of organs; corresponding to them are heterotopies, in the morphological aspect, and saltations, in the evolutionary sense; (2) dedifferentiation of the organs (the shift of one ontogenetic program onto various organs); (3) transitive polymorphism (conservation in diversity of a certain organ during phylogeny). These processes probably serve to indicate that rearrangement in the functions of the regulatory genes played an important role in the evolution of gymnosperms. /// Для фруктификаций голосеменных введена собственная система морфологических понятий. Путем аналиэа наиболее иэученных ископаемых родов родов по комплексу приэнаков получены конгрегации раэного ранга (семейства, порядки и классы). Прослежены филогенетические преобраэования раэных органов. Установлена новая крупная филогенетическая ветвь (класс Ginkgoopsida), идущая от Calamopityales (нижний карбон) к Callistophytales и далее к Peltaspermales, от которых проиэошли порядки Ginkgoales, Leptostrobales (=Czekanowskiales) и Caytoniales. Порядок Arberiales (глоссоптериды), видимо, проиэошел от Calamopityales. У всех гинкгопсид сохраняется обший тип семян, платиспепмических, бескупульных, с двумя проводящими пучками в интегументе. В классе Cycadopsida удержались радиаспермические семена. В линии от Lagenostomales к Trigonocarpales радиально-симеетричная купула преобразовалась в интегумент с той же симметрией. Древние лагеностомовые с билатерально-симметричной купулой дали начало Cordaitanthales, при этом купула превратилась в билатерально-симметричный интегумент. У Pinopsida (Cordaitanthales, Pinales) семена вторично-бескупульные н вторично-платиспермические. Их васкуляризация постепенно редуцировалась. Предполагается, что семена покрытосеменных первично-радиоспермические с радиальной купулой. Предков покрытосеменных надо искать в классе Cycadopsida. Показано распределение филогенетических ветвей в системе фитохорий геологического прошлого. Основные эволюционные новообразования происходили в экваториальном поясе и прилегающих к нему экотонах. В филогении голосеменных большую роль играли (1) гомеотические преобразования органов, приводившие к гетеротопиям и сальтациям; (2) дедифференциация органов (распространение одной онтогенетической программы на разные органы); (3) транзитивный полиморфизм (сохранение разнообразия органов в ходе филогении). Эти процессы, видимо, связаны с перестройками в работе регуляторных генов.

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