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STUDIES IN THE CALENDULEAE
491
In regard to the morphology of the achenes, the subgenus Tripteris
represents a particular line of evolution in Osteospermum. In the species
that I have placed in this suhgenus the achenes are nol only 3-winged
hut also furnished with a closed apical cavily or air-chamber (I p. 273,
figs. 25a, c; p. 290, fig. 28a). I consider tliis apical air-chamber to be
a further specialization for wind dispersal, for it reduces the specific
weiglit of the achenes. It is found in various stages of development in
different species of Ihe subgenus Tripteris. The smallest apical
air-eavily is met with in Osteospermum amplectens and O. breviradiatum.
There it is so minute as to be hardly visible to the naked eye (I p. 341,
fig. 35 d). In other species it may be so large that its si/.e amounts to
a Ihird or to nearlv half the space of the seed-cavitv (I p. 290, fig.
28 a; ]). 337, fig. 34 b). Only the winged achenes of the species belonging
10 the subgenus Tripteris are equipped with an apical air-cavity. In
some species a few wingless achenes il—3) are found together with
the winged ones in the heads, hut these alwavs lack such an
air-chamber.
Particularlv remarkable is the morphology of the achenes in
Osteospermum eulendulaeeum L. f. mon Harv.) in sect. Oligocurpus. This
species so extremelv rich in biotvpes is characterized by very great
heterocarpism and holds an intermediate position between the
sub-genera Euosteospermum and Tripteris. for il comprises biotvpes both
with and without an apical air-chamber and ils wingless achenes may
also be furnished with such an air-cavity |I p. 348. figs. 36 d, f, 1).
In respect of ils heterocarpism, this species is as far advanced as llie
Calendula species.
The rostrate achenes constitute an interesting tvpe. Their name is
due lo the fact that their apical part is möre or less stronglv produced
into a beak. These achenes are terete |l p. 277. fig. 26 b; p. 283, fig.
27 Ii; p. 348, figs. 36 c, f, k) or möre rarely 3-ribbed or 3-angled
11 p. 211, fig. 20 e). They appear sporadically together with other types
of achenes in the two subgenera of Osteospermum and in Calendula.
The occurrence of these achenes is of no or lillie taxonomic vallie, but
|hey are of interest because they suggest a close relationship between
Osteospermum and Ctdendula just as do the three-winged achenes.
In South Africa rostrate achenes occur in only a very few species
in the tribe C.alenduleae, namely in some Osteospermum species, bill
in the Mediterranean region such achenes are found in most of its
species. They never arise alone in a head, bill alwavs logether with
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