These features refer to the tenth leaf stage. The tenth leaf is the tenth true leaf produced after the cotyledons. On seedlings with alternate or spirally arranged leaves it is just simply the tenth leaf produced. On seedlings with opposite leaves it is one of the leaves in the fifth pair of true leaves produced. On seedlings with whorled leaves it will be one of the leaves in the appropriate whorl; e.g. if there are four leaves in each whorl then the tenth leaf will be one of the leaves in the third whorl.
An intramarginal vein is a vein of constant thickness (much thinner than the
midrib) just inside the margin and extending from the base to the apex of the
leaf blade (or leaflet blade in the case of compound leaves). Lateral veins run
from the midrib to the intramarginal vein. To be classed as an
intramarginal vein rather than looping lateral veins there should not be any
major bends. However, slight indentations may occur at the junction with
the main lateral veins.
This character is not applicable to leaves or leaflets with longitudinally parallel venation.