Salient features, floral diversity, diversity of families and phylogeny of the following orders: Ranales, Centrospermae, Amentiferae

Salient features, floral diversity, diversity of families and phylogeny of the following orders: Ranales, Centrospermae, Amentiferae:-

Ranales:-

> Ranales is a natural taxon. It is characterized by the parts typically spirally arranged (cyclic in advance member), numerous, distinct, the perianth often not differentiated into calyx and corolla. Gynoecium is apocarpous and multicarpellate (i.e., composed of many unilocular unicarpellte pistils).

> Ranales have been considered as the most primitive due to the absence of vessels in large number of families like Alismataceae. Magnoliaceae, Winteraceae etc. Peculiar floral morphology, anatomy as well as binucleate pollen at the time of release from the microsporangium in several families like Magnoliaceae, Ranunculaceae, Winteraceae etc.

> Benthum and Hooker (1862-83) kept this order at the starting of classification. Ranales of Benthum and Hooker comprises eight families: Ranunculaceae, Dilleniacea, Calycanthaceae, Magnoliaceae, Annonaceae, Menispermaceae, Berberidaceae and Nymphaeaceae. It is characterized by numerous floral parts, especially stamens and carpels; floral parts arranged in spiral, cyclic or hemicyclic manner with hypogynous flower.

> Key to the Families of Ranales:-

Centrospermae:-

> Centrospermae is a taxon usually characterized by haplochlamydous and sometimes

diplochlamydous flowers, basal or free central (with reference to the name of order) axile

placenta (in which partition walls are dissolved), unilocular ovary, campylotropous ovule

and seed with coiled or curved embryo and perisperm.

> It is also called Curvembryae due to presence of curved embryo. The Centrospermae (Caryophyllales) group represents one of the most controversial orders in the Angiosperms. For a very natural group the term Centrospermae is given by Eichler (1876).The curved campylotropous ovule frequently becomes a kidney shaped seed round the wall of which lies the embryo.

> There are some other characterstic features also found like superior ovary, single whorl of perianth, P-III sub type of sieve element plastid and Betalins (Except Molluginaceae and Caryophyllaceae).

> Bessey designated the order as Caryophyllales and supported its Ranalian ancestry indirectly through Rosales; in the Caryophyllales he included the families Podostemaceae and Salicaceae.

> Eichler (1876) included following orders as follows-

Order-1. Oleraceae: Includes family Polygonaceae, Nyctaginaceae, Chenopodiaceae and Amaranthaceae.

Order-2. Caryophyllales including single family Caryophyllaceae.

Order-3. Oputinae which includes families Phytolaccaceae, Portulacaceae, Aizoaceae and Cactaceae.

> Centrospermae order of Engler and Prantl (1897-1915) included the families Aizoaceae, Amaranthaceae, Chenopodiaceae, Nyctaginaceae, Phytolaccaceae, Cactaceae, Basellaceae, Caryophyllaceae, Cynocrambaceae and Portulacaceae. After some time Engler (1924- 1936) separated the family Cactaceae and converted into order Opuntiales of single family Cactaceae.

> Mabry (1976) classified the order Centrospermae or Caryophyllales on the basis of all available data from different disciplines like morphology, embryology, serology, ultra structural etc. into two sub order and 11 families.

1. Sub-order: Chenopodinae includes families like -

(i) Aizoaceae

(ii) Amaranthaceae

(iii) Basellaceae

(iv) Cactaceae

(v) Chenopodiaceae

(vi) Didiereaceae

(vii) Nyctaginaceae

(viii) Phytolaccaceae 

(ix) Portulacaceae

2. Sub-order: Caryophyllinae includes only Caryophyllaceae and Molluginaceae.

> The families of sub order Chenopodinae contains a unique N-containing pigments the Betalins and the other two families of sub order Caryophyllinae shows Anthocyanins.

> There is some evidence of ultra-structural research on sieve-tube plastids (Behnke and Turner, 1971; Behnke, 1976) and pollen morphology (Nowicke; 1976; Skvarla and Nowicke, 1976) has revealed the close relation between the betalin families and the Caryophyllaceae and the Molluginaceae.

Amentifereae:-

>The group Amentiferae (Catkin possess scaly bract, usually flexuous spike or spike like inflorescence) are characterized by trees or shrubs, flower small, unisexual, at least the staminate in elongated catkins, Anemophilly and exalbuminous seeds. Distribution occurs mainly in the North temperate Zone. Catkin (Ament) is a scaly bracteated, usually flexuous spike or spike like inflorescence of cymules.

> It is a distinctive order with the characterstics of its single family, Salicaceae. There is much evidence that the family has been derived from advanced ancestral stocks. The order Salicales through Fagales were designated by Eichler (1883) as a single order, Amentiferae. They were accepted as a phyletically homogenous group of primitive Dicots by Engler and Randle, both of whom rejected Eichlers’s name and considered them to represent several orders.

> Hutchinson transferred all these amentiferous orders (Plus the Urticales) to a phyletic position that treats them as these descendants of hamamelidaceous ancestors. The plants were restudied by Hjelmquist (1948) and treated by him as a natural assemblage of several orders comprising a single taxon, Amentiferae.

> Plants are deciduous trees or shrubs. 

> Leaves are simple, alternate, stipulate and deciduous.

> Flowers are small in size and unisexual, those of each sex in dense erect to pendulous catkins, each flower subtended by a scale (or bract). 

> Perianth is absent or vestigial, represented by a copular disk or small nectary. 

> Male flowers are represented by 2-30 stamens, free or connate Female flowers having 2-4 unilocular carpels, with numerous ovules. 

> Placentation is parietal or basal with inferior ovary. 

> Anemophilous type of pollination is found. 

> Fruit is 2-4 valved capsule. 

> Seeds exalbuminous covered with silky hairs arising from the funicle.