. Bulletin of the British Museum (Natural History) Botany. . Fig. 17 Corolla aestivation in pentamerous members of the Guttiferae: (a) quincuncial (as in Theaceae); (b, c) intermediate forms (as in Triadenumfraseri); (d) contorted (as in Hypericum). can be observed in H. frondosum (sect. 20. Myriandra) (see p. 198). The numbers of members in these two whorls are almost always the same; only very exceptionally has an extra petal been recorded ( in H. papuanum, sect. 26. Humifusoideum, and H. empetri- folium, sect. 19. Coridium). (b) Form A consequence of the constantly contorted aestivation
. Bulletin of the British Museum (Natural History) Botany. . Fig. 17 Corolla aestivation in pentamerous members of the Guttiferae: (a) quincuncial (as in Theaceae); (b, c) intermediate forms (as in Triadenumfraseri); (d) contorted (as in Hypericum). can be observed in H. frondosum (sect. 20. Myriandra) (see p. 198). The numbers of members in these two whorls are almost always the same; only very exceptionally has an extra petal been recorded ( in H. papuanum, sect. 26. Humifusoideum, and H. empetri- folium, sect. 19. Coridium). (b) Form A consequence of the constantly contorted aestivation of the petals in Hypericum is that, in a given flower, the same margin of each petal is outside in bud. It may be this relationship that has resulted in the development of asymmetry in the petals, a character that is absent in all allied genera except Santomasia (and Cratoxylum, where it is sometimes slightly developed). This asymmetry is always evident to some extent, except (i) in the smaller, reduced flowers ( of//, humifusum, sect. 14. Oligostema or H. japonicum, sect. 30. Spachium) and (ii) in some flowers with a pseudo-tubular corolla (sects 25. Adenotrias, 30. Elodes). In other, less highly evolved species the inner and outer margins are always distinguishable. The line of the outer margin is frequently interrupted by a notch or indentation, which results in a more or less evident projection. This marks the limit of the part of the margin that is actually outside in bud and has been termed the apiculus (Robson, 1970). Even when an apiculus is not visible, the corresponding point on the margin (which is the morphological apex) is usually recognisable from the pattern of venation and glands. It marks the end of the midrib, which divides the petal into two, usually unequal, parts: (i) an outer, usually thicker and smaller part with denser venation and glands more often laminar, and (ii) an inner, usually larger and thinner part with laxer venation and glands more often
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