Family: Platanaceae J. Leslib – ex Dumort, 1829
2/ Descriptions: a/ Habit:
Plane trees are deciduous, large and mesophytic (site 1).
They grow in moist woodlands, especially on stream banks and steep woody slopes. Other species grow best on drier rocky soils. The exact ecological range is unknown for most species. Nevertheless, they are frequently found in mineral-rich soil (site 2).
Photo 3: site 1
Plane trees produce glossy, bright green, maple-like leaves having 3 to 5 shallow lobes (site 2). Those leaves have a medium or a large size, and are alternate, flat, petiolate (the petiole base enclosing the axillary bud), and simple. The lamina is nearly always dissected and palmately or pinnately veined. Leaves are moreover stipulated, scaly and caducous. Vegetative buds are scaly too (site 1).
(Photo 4: site 3)
c/ Inflorescences: Flowers are aggregated in ‘inflorescences’, consisting in globose, sessile or pedunculate heads of flowers; each inflorescence is exclusively either male or female. This tree is in fact a monoecious anemophilous plant (site 1).
Floral formula for males’ flowers: K? C? A3-5 G0 and for females’ ones: K3 C0 A0 G5-9. Flowers are small, regular, cyclic and either bracteate or ebracteate (depending on the interpretation of the ‘scales’). The perianth presents distinct calyx and corolla (or at least, so interpretable, in male flowers), or sepaline (the female flowers lacking any semblance of a corolla). Corolla in male flowers is tiny or vestigial and polypetalous (site 1).
(Illustrations 1 & 2: Platanus’ male and female flowers, site 1)
All the androecial members are free of the perianth, equal and free of one another. The androecium is exclusively composed of fertile stamens, that have a very short filament and basifixed, tetrasporangiate and biloculate anthers (site 1).
The Gynoecium’s carpels are isomerous with the perianth, or increased in number relative to the perianth. It is moreover apocarpous and superior. Carpels are incompletely closed, non-stylate. This family presents an apical to marginal placentation (site 1).
The fruit of plane trees are non-fleshy, one seeded and aggregated. The fruiting carpel is indehiscent, achene, or nucular. Gynoecia of adjoining flowers are combining to form a multiple fruit that have a circle shape. What’s more, endospermic seeds give a well-differentiated embryo (site 1).
(Photo 5: P. orientalis, site 3)
3/ Geography: These trees live under a temperate climate. They are localized in areas such as North America, Southeast Europe, Southern and Eastern Asia (site 1).
4/ Representative genera and species: Only 1living genera, including 10 species, can be counted, (genus, Platanus) (site 1).
We can name the most famous: P. acerifolia (London Plane Tree) & var. pyramidalis; P. occidentalis (American Plane Tree); P. orientalis (Oriental Plane Tree)(see photo 3); P. cuneata; P. racemosa (California Plane Tree); P. Wrightii (site 2).
5/ Economical interests:
Plane trees are principally used for timber (site 4).
Family: Urticaceae Juss, 1789
2/ Descriptions: a/ Habit: This family groups shrubs, lianas, a few trees and herbs occasionally with stinging hairs. Those plants are non-succulent and mesophytic. In addition to these characteristics, they can be self-supporting plants or climbing one (site 1 and 2).
Leaves can be small to large, alternate or opposite. Urticaceae’s leaves are usually petiolate, non-sheathing, simple and stipulate. The lamina is mostly entirely or rarely dissected (when it is the case, the plant is pinnately or palmately veined.). Lamina margins are entire, serrate or dentate. Urticating hairs are present for the Urticeae, or absent (site 1).
(Illustration 3: Urtica urens., site 1)
The numerous flowers are very often aggregated in ‘inflorescences ’on short axillary.The flowers are mostly all of the time condensed into heads, or sometimes crowded on a common receptacle, which may be concave or convex. Here too, flowers are either male or female. Plants belonging to this family can be either monoecious dioecious, but are all anemophilous (site 1).
(Photos 6 & 7: male and female inflorescences of Urtica dioica, site 3)
Floral formula: K4-5C0 A4-5 G0 for males’ flowers and K3-5 C0 A0 GS1 for females’ ones (site 5).
Flowers are small bracteate or ebracteate and regular. Moreover, the hypogynous disk is absent.
Perianth is sometimes vestigial to absent in female flowers. The calyx (the perianth being thus interpreted) is polysepalous or gamosepalous, regular (site 1).
(Illustrations 4 & 5: Nettles’ flowers diagrams, site 1)
Androecial members are free of the perianth and free of one anotherand are exclusively fertile stamens that are isomerous with the perianth, oppositisepalous and filantherous (the filaments is usually wrinkled). Furthermore, anthers are tetrasporangiate and the pollen grains 2-celled.
The gynoecium is ostensibly 1 carpelled, monomerous or syncarpous and in addition, it is usually superior. This carpel is shortly stylate (only one style), or non-stylate and contains 1 ovule. The stigmas (1 or 2 usually), have the dry type and are papillate. In this family, placentation is basal (site 1).
Urticaceae’s fruits are fleshy, or non-fleshy and one seeded. The fruiting carpel (treated as monomeric) is indehiscent; small achene, nucular, or drupaceous. If the fruit is recognized as syncarpous, it is then considered as indehiscent (site 1).(Illustrations 6, 7 & 8: Nettles’ fruit, site 1)
In comparison to the Platanaceae, the gynoecia of adjoining flowers are not forming a multiple fruit (site 1).
3/ Geography: Those plants are met in temperate to tropical areas. Actually Urticaceae are relatively cosmopolitan and except in frigid zones, they are present everywhere in such climates (site 1).
4/ Representative genera and species:
We can distinguish 49 genera including 550 different species. Here are for instance some of the genera: Aboriella, Achudemia, Archiboehmeria, Astrothalamus, Australina, Boehmeria, Chamabainia, Cypholophus, Debregeasia, Dendrocnide, Didymodoxa, Discocnide, Droguetia, Elatostema, Forsskaolea, Gesnouinia, Gibbsia, Girardinia, Laportea (photo 2), Lecanthus, Leucosyke, Maoutia, Meniscogyne, Myriocarpa, Nanocnide, Neodistemon, Neraudia, Nothocnide, Obetia, Oreocnide, Parietaria, Pellionia, Petelotiella, Phenax, Pilea, Pipturus, Poulzolzia, Procris, Rousselia, Sarcochlamys, Sarcopilea, Soleirolia, Touchardia, Urera, Urtica (photo 6 & 7, illustration 3)(site 1).
Photo 8: Pilea cadierei (site 3)
Photo 9: Boehmeria nivea (site 3)
5/ Economical uses:
A commercial cordage fibre (ramie) is obtained from Boehmeria nivea (site 20. A few (Pilea spp.) are grown as novelties, and nettles (Urtica spp.) constitute edible and quite palatable greens (site 1). Thus, in India, fruits, roots and leaves of such plants are very often eaten (like Poulzolzia tuberosa)(site 4). Finally, we must not forget that some of the members of this family are used as ornament.