MORPHOLOGY OF THE CROP PLANT, VARIATION IN PLANT PARTS IN DIFFERENT SPECIES
Detailed morphological descriptions of most of the Nicotiana species have been given by Goodspeed (1954) in his monograph `The Genus Nicotiana' and 5 new Australian species by Burbridge (1960). Hence, the description here is confined only to N. tabacum and N. rustica, the two species of commercial importance.
Both species have got a sturdy or more or less woody habit of growth with evenly spaced leaves. The leaves of N. rustica are usually petiolate and of regular ovate or cordate shape with a dark green, shiny surface. Sessile, ovate or oblong-lanceolate shaped leaves are most common in N. tabacum. N. tabacum types are taller than rustica types. The inflorescence is usually a compact `Thyrse' represented by a thickened central axis, shortened branches and monopodial-sympodial development of peripheral flowers. Tabacum is semi-xerophytic to mesophytic whereas rustica is a mesophyte. In rustica the leaves are thicker, dark green and have uneven surface.
In N. rustica the pedicels are short at first (3-4 mm long) but extend to more than 6 mm when the flower opens. Calyx cylindrical, pubescent, membranous and narrow with pointed sepals with a longer odd sepal. Corolla greenish yellow, 1.2-1.5 cm long, pubescent with tube proper 3 mm long and 2 mm wide. Throat broadly obconic with contraction near the mouth. Stamens white, with four of them long and one short. Capsule elliptic, ovoid or subglobose, 7-15 mm long. Seeds elliptic, oval and dusky brown.
In N. tabacum the pedicels are 5-10 mm long during early stages but elongate to 10-20 mm later. Floral calyx cylindric or cylindric campanulate; 12-20 mm long. Sepals triangular, acuminate, shorter than calyx tube, unequal in length. Corolla pubescent on the outer surface and tube proper 10-15 mm long and 2-3 mm wide, throat 25-40 mm long, lower half cylindric, pale green or creamy, upper half similar in colour or pink to red, expanded into deep cup 7-12 mm wide. Limb 10-15 mm wide lobed or pentagonal, white, pink or red, stamens inserted on base of corolla throat, erect with 4 long and 1 short stamen. Capsule narrow, elliptic, ovoid or orbicular, acute or blunt 15-18 mm long. Seeds nearly spherical or elliptic and light brown.