Ontogeny of the Calliandra – massulae (Mimosaceae: Ingeae), and the associated viscin body

Polyads, called also massulae, are common in the Mimosaceae. Within this family, only in Calliandra (s. l.) polyads show a remarkable morphological variation: 16-grained lens-shaped massulae in the neotropical Zapoteca (syn. Calliandra p.p.), and highly asymmetric eight-grained massulae in Calliandra (s. str.). As a further specialisation the massulae in Calliandra (s. str.) possess a sticky appendage called a viscin body. The form and ontogeny of this unique two-dimensional construction of the massula is of particular interest. In Calliandra (s. str.) the octad is normally the developmental product of the initiation stage, beginning with one pollen mother cell (PMC). In total, Calliandra (s. str.) possesses eight PMCs in each anther.The dicotyledons are characterised by the simultaneous type of cytokinesis, but wall formation in Calliandra (s. str.) during meiotic division is successive, as common in monocotyledons. The first wall divides the PMC diagonally, and during the tetrad period, two clear variants of tetrads are found. One shows the typical rhomboidal arrangement and the other forms two congruent symmetrical halves. The latter probably results from early fixed, quite inflexible walls. The cells of tetrad do not separate, and four successive mitotic divisions give rise to the eight-celled massula. The direction of growth of the PMC and the massula, the sequence of division, and the position of the walls all show a strict polarity. The normal number of eight cells in each massula is sometimes exceeded without loss of viability.Calliandra (s. str.) lacks a developed “Pollenkitt”, and its asymmetrical massula is combined with the viscin body, which is involved in pollination. This viscin body is located on a specialised pollen grain at the top of the massula. With the viscin body, Calliandra (s. str.) massulae have a mechanism for immediate and persistent attachment to different surfaces. SEM is used to understand the mechanisms of attachment in detail. Furthermore, the relation between pollinators and the massula shape is investigated. Massula transport and the role of the viscin body in pollen–stigma interaction are discussed as well. The stigma of Calliandra (s. str.) is papillate and in the receptive stage, it is characterised by acquisition of a copious exudate.Zapoteca (syn. Calliandra p.p.) massulae could be distinguished histochemically from those of Calliandra (s. str.) by the main components of the “Pollenkitt”. Histochemical and physical properties of the viscin body suggest a waxy nature, including lipids in combination with unsaturated fatty acids. Proteins are present in less amounts and polysaccharides and polyglucans are absent. These results are discussed in relation to analogous phenomena in other families.The term “apex cell” is introduced to indicate the specialisation of the tip-cell of the massula by ontogeny and polarity.