In this article we will discuss about:- 1. General Features of the Juglandaceae 2. Floral Range in the Juglandaceae 3. Position and Affinity 4. Number and Distribution 5. Commonly Occurring Plants 6. Economic Aspects.
General Features of the Juglandaceae:
Habit – Shrubs or trees, resinous, aromatic.
Leaves – Alternate or opposite, imparpinnate, exstipulate.
Inflorescence – Catkins.
Flowers – Unisexual.
Perianth – In male flowers, 3- to 6-parted and in female 4-parted.
Androecium – Stamens 3-100; anthers basifixed.
Gynoecium – Carpel 1; ovary inferior, 1-locular, style short; stigma plumose.
Fruit – Drupe-like nut, surrounded by a leathery or fleshy husk.
Seeds – Embryo very large; cotyledons fleshy, 4-lobed, foliaceous or corrugated; endosperm none.
Floral Range in the Juglandaceae:
The Juglandaceae shows variations in the type of catkin and floral organisation. In the first type, the inflorescence is a panicle of clustered erect or pendulous male catkins associated with a female central catkin, e.g., some species of Engelhardtia and Pterocarya. In the second type, we find a solitary terminal pendulous female catkin which, by way of reduction, conforms to a few flowered erect spike (Carya, Juglans). The third type is a triclustered male catkin on old wood, as in Alfaroa. The fourth and last type takes the form of a simple lateral male catkin, as in some species of Juglans.
The male flowers show a wide range in the development of perianth as well as in the number of stamens. The perianth is absent in Carya; here the stamens are 4-10, but sometimes 2 or 3. In Juglans, the perianth is 3- to 4-parted; here the stamens may be 20 in the lower flowers of the catkin and 6 or 8 in the upper flowers. Pterocarya is in possession of 4-parted perianth, with stamen number varying between 8 and 16.
The structure and development of female flower as well as the relation of ovule to carpel has been a subject of dispute. According to van Tieghem, the vascular supply to each floral leaf comes out from the stem stele at the base of the flower; hence, the ovary is superior and not inferior. Nicoloff stated that the ovule is a development from the apex of floral axis and the carpels do not contribute to its formation.
Benson and Welsford (1909) suggested that the ovule is parietal and anatropous. Nast (1935) interpreted the ovule as a modified axile type. Manning (1940) contended that the ovule is derived from an axile condition where the ovules are clustered near the centre of a normal or incomplete partition. If a macroscopic examination of the young ovary is made, the ovule will appear basal and orthotropous.
As to the position of the carpels, it is either median (Engelhardtia, Juglans, Pterocarya) or transverse (Carya, Pterocarya).
The bract and a pair of bracteoles are united to various degrees. In Engelhardtia, the bract and bracteoles are united at the base of the ovary to form a trilobed wing in the fruit. In Juglans, the bract is united to a little above the ovary and the bracteoles are united still higher to constitute a toothed rim. The bracts and bracteoles are almost free in Pterocarya; here the bracts disappear in the fruit, but the bracteoles form a broad wing in the centre.
Position and Affinity of the Juglandaceae:
The phyletic position of the Juglandaceae has been debated at length. Both Bessey and Hutchinson felt that the family evolved from one of the members of the Sapindales. However, Hutchinson (1969) changed his mind and regarded the supposed affinity of the family to be superficial. “The absence of stipules from Juglandaceae is somewhat disconcerting, for most of the immediate family stocks from which they seem to have been derived have stipulate leaves”.
In view of the fact that stipules are very rarely present in the Caesalpinioideae and are not even constant in the Rosaceae, they have been suppressed in the Juglandaceae. The family has been included in the Terebinthales by Hallier on the basis of its origin from the Rutaceae.
Anatomically, according to Tippo (1938), the family is much more advanced than indicated by Engler’s treatment. From the view-points of wood anatomy and pollen morphology, Heimsch (1942, 1944) reported that the family is not allied to the Anacardiaceae and Julianiaceae. Hjelmqvist (1948) placed the Juglandaceae as advanced over the Myricaceae.
Lawrence (1951) suggested that the Juglandaceae is closely related to the families under the Urticales; his idea is based on the resinous condition, pinnate leaves and floral morphology. Core (1955) believed that the family is akin neither to the Salicales nor to the Fagales. Benson (1957) opined that the family is of common origin with the Hamamelidaceae.
Number and Distribution of the Juglandaceae:
A family of about seven genera and 50 species, the Juglandaceae abounds in the north temperate regions and mountains of the northern tropics.
Commonly Occurring Plants of the Juglandaceae:
Engelhardtia spicata Bl. and Juglans regia L. are large trees; the former is found in subtropical Himalaya and the latter in temperate Himalaya.
Economic Aspects of the Juglandaceae:
The Juglandaceae is of considerable economic importance. The seeds are rich in oil and several species are edible, e.g., Pecan Nut (Carya, illinoinensis), Hickory Nut (C. laciniosa, C. ovata), Mockernut (C. tomentosa) Butternut or White Walnut (Juglans cinerea), Black Walnut (J. nigra) and English Walnut (J. regia). The species of Carya, Engelhardtia and Juglans produce valuable timber. The species of Pterocarya are raised for their ornamental value.
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