Alternate leaves originate from different points along the stem/branch:

In some cases they are widely spaced, in other cases, such as the 'leaves' of Lycopodium, they are arranged in dense spirals:

A particular case is that of several plants whose alternate leaves are, at least in part, arranged in a dense rosette at the base of the stem; they should be not confused with whorled leaves (see later):

Opposite leaves are arranged in pairs on the two opposite sides of the stem/branch:

One of the most frequent mistakes by beginners is to attribute the character 'leaves opposite' to the arrangement of leaflets in compound, pinnate leaves (which can be alternate):

Whorled leaves are arranged in groups of 3 or more originating from the same point on the stem...:

...such as in many species of Rubiaceae... the genus Erica...:

...or in the genus Myriophyllum:

In some plants the upper leaves are opposite, the lower leaves alternate (or vice-versa), or the leaves are 'sub-opposite' (not perfectly opposite and hence arrangement not very clear). In such cases the species can be reached by selecting both the option 'leaves opposite' and the the option 'leaves alternate':

Plants without leaves: some plants are devoid of well-developed leaves, the photosynthetic function being carried out by modified stems:

Among them are the horsetails (genus Equisetum), in which the leaves are reduced to membranous sheaths...:

...the opuntias, with leaves transformed into acicles...

...the species of Ephedra and Casuarina , with leaves transformed into short, inconspicuous sheaths...

...and several parasitic or saprophytic species which do not need true leaves since they are devoid of chlorophyll, such as those of the genus Cuscuta:

The species of Ruscus and Asparagus have modified stems which may resemble true leaves, called 'cladodes': they can be reached by selecting both the option 'plant with leaves' and the option 'plant without leaves':