Irmgard Jäger-Zürn

Crustose root and root-borne shoots of Zeylanidium olivaceum (Podostemaceae - Podostemoideae): Part VI of the series 'Morphology of Podostemaceae'

Summary The study presents new data about the developmental morphology of vegetative and floral structures of Zeylanidium olivaceum (G ard .) E ngler , a crustose representative of Podostemaceae. The renewed debated nature of the crust (root versus thallus) is clarified. The root nature is evidenced by (1) the existence of a fringe of root cap cells, (2) the presence of an inner meristem, responsible both for the growth of the root and the root cap cells, (3) lack of leaves (aphylly), and (4) the endogenous development of secondary (root-borne) shoots. Secondary shoots occur in the form of floriferous and vegetative shoots. They all grow plagiotropously and are orientated towards the respective front of the growing crustose root. The axes are zygomorphic, with the leaves being unilateral at their bases and asymmetrical in shape. The floriferous shoots are distichously foliated; but instead showing a 180° phyllotaxis, the leaves arise in a divergence angle of about 25° to 30°. The leaves, therefore, form two nearly parallel rows on the upper side of the plagiotropous shoot axis. The axes of the vegetative shoots are inconspicuous, remain within the crustose root and are more or less confined to a tiny shoot apex, from which the leaves develop. The leaves are filiform, and only they become visible above the surface of the crust. They are basally fused to the crust as well as to each other, resulting in a short compact zone at the basis of the tuft. The phyllotactic pattern is the same as in the floriferous shoots. Secondary (floriferous and vegetative) shoots as well as the upright growing primary shoot thus differ markedly from each other (shoot polymorphism). The syncarpous gynoecium of the flower consists of two carpels which are equal in size and not unequal as described in the literature. But they are positioned at different levels on the axis, being seemingly shifted against each other.

The unusual ramification mode of Sphaerothylax abyssinica (Wedd.) Warm. (Podostemaceae - Podostemoideae): Part VIII of the series ‘Morphology of Podostemaceae’

Summary The unusual subfoliar position of branches described in Podostemum subulatum (J ager -Z urn 1999) is confirmed in a second representative of Podostemaceae - Podostemoideae: Sphaerothylax abyssinica . The branch emerges from the mother shoot, but develops within the superpositioned leaf that is connected with branching. After detachment of the branch from the leaf, a cavity is left at the reverse (dorsal) side of the leaf. It resembles the sheath at the ventral side of the leaf (which surrounds the axis of the mother shoot) and is thus called an additional (dorsal) sheath. It sheathes the daughter shoot. The leaf thus achieves a dithecous (double-sheathed) shape. Peculiarly, the additional sheath is placed at the side of the median plane of the leaf. This is in contrast to the median position observed in Podostemum subulatum . The condition of Sphaerothylax abyssinica may be seen as a transition to the usual axillary type. Ramification of shoots only occurs in connection with flowering. The inflorescence is a cyme. Basal parts of shoot axes and leaves are fused to each other. This phenomenon, called ‘syndesmy’, is the cause of a compact plant body, especially concerning the inflorescence. Syndesmy sufficiently explains why shoot axes and leaves in Podostemaceae have the appearance of transilient structures without clear demarcations.

Morphology and morphogenesis of ensiform leaves in Apinagia multibranchiata and Mourera fluviatilis (Podostemaceae: Podostemoideae)

Summary The leaves of Apinagia multibranchiata and Mourera fluviatilis , both Podostemaceae, are transversely inserted. The base (lower leaf zone, Unterblatt) is developed as a bifacial sheath with true leaf margins. The upper leaf zone (Oberblatt) resembles an ordinary leaf lamina with lanceolate or fan-like shape, but it is of ensiform structure due to intercalary extension growth proceeding from the dorsal (abaxial) side of the leaf. In both species, the ensiform blade has undergone a superimposition in the form of a circinate coiling of the growing tip toward the ‘front side’ of the dorsiventral plant body perpendicularly to the sheath as well as an involute bending of both edges of the ensiform blade toward the ‘front side’. Similar leaves of ensiform structure, even dissected or with hairy outgrowths on one side of the blade, occur also in some other (bothNew and Old World) species of Podostemoideae, whereas another group of related species in the subfamily develops compound leaves of the ordinary type. This difference, not clearly recognized so far in the literature, is certainly of taxonomic importance.