Botanical Journal of the Linnean Society, 72: 115‑148. With 8
plates and 3 figures
Reproduced here with the
permission of the author
The floral anatomy of Victoria Schomb.
E. L. SCHNEIDER
OBSERVATIONS - Continued
to the dorsal carpellary regions and the
From the upper, outer margin of the vascular plexus, there arise a number of large vascular bundles (Fig. 1). Following the terminology of Moseley (1961) for Nymphaea, these bundles will be termed gynoecial vascular strands. When the gynoecial strands separate from the plexus, they are very large and few in number. As they slope downward and outward beneath the gynoecial locules, radial divisions occur in such a manner that the outer gynoecial wall is supplied with an ample number of gynoecial vascular strands. Generally, the number of gynoecial strands corresponds to the number of locules. Following their pathway from beneath the locules, and ascending the outer wall, it becomes apparent that the strands do not usually lie along the same radii as the locules, but frequently lie along the radii of the septa or in positions intermediate between the locules and the septa. Observations of the gynoecial strands below the locules reveal that each strand is composed of two collateral, normally orientated bundles. Each pair of bundles lies along one radius with the bundles in contact, one above the other. The adaxial bundle of each gynoecial strand typically has its phloem extremely reduced. This arrangement is maintained as the strands ascend the outer gynoecial wall. Following their upward course, branching commonly occurs between adjacent gynoecial strands.
supply to the dorsal carpellary region typically has its origin from the inner
bundle of the gynoecial strand. From its origin at the receptacular plexus to
the distal locular regions, the inner bundle branches radially, either
supplying the septa directly or first forming distinct supernumerary bundles (Fig.
1). It is not uncommon, however, for the supernumerary bundles to be formed
from divisions of both bundles of the gynoecial strand, whereby each bundle in
the strand undergoes an oblique-radial division. Since the two bundles of the
strand are in contact, the resulting branches appear as one larger bundle. As
the supernumerary bundles extend beneath the dorsal carpellary region,
branching occurs, with each resulting branch supplying the nearest septum. The
supernumerary bundles that arise toward‑ the more distal carpellary
regions commonly remain double. Together with the single bundles that are
radial branches of the inner bundle of each gynoecial strand and the similarly
formed ventral carpellary bundles, they form a reticulum in the septa (Fig.
1, Plate 8A).
The reticulum consists of several small, variously orientated vascular bundles.
Each anatropous ovule receives its single vascular supply from the reticulum.
Distal to the locular region, the gynoecial wall becomes constricted (Plate 2B, Fig. 1). Within this region, each gynoecial strand pursues its upward course and supplies the remaining appendicular organs. In addition, each gynoecial strand supplies vascular branches to its corresponding stylar process. These vascular supplies arise at various levels; and, at any one level, each consists typically of two bundles. These two bundles, one of which is derived from the inner bundle of a gynoecial strand and the other from the outer bundle, commonly show a recurrent pattern as they supply the stylar process (Fig. 1), a pattern that reflects the differential growth between the stylar processes and the peripheral, ensheathing appendicular tissue. These recurrent bundles terminate directly in the stylar process. Occasionally, the inner branch of each recurrent bundle anastomoses with the ventral carpellary veins or branches of these and, together, terminate in the stylar processes. The inner bundles of the gynoecial strands are best interpreted as dorsal carpellary vascular bundles, since they not only supply branches (along with the ventral carpellary bundles) to the carpellary regions, but also typically correspond in number to the number of locules and stylar processes.
Traces to each of the four sepals arise from (1) either the lower portions of the vascular plexus or the major peduncle strands immediately below the plexus and (2) the small peripheral bundles of the outer ovary wall. The latter small bundles represent the continuation of the smaller bundles of the peduncle peripheral system. All traces to the sepals consist of collateral normally orientated bundles. In both V. amazonica and V. cruziana, the sepal supplies commonly depart from the lowest 'portions of the plexus (Fig. 1). These traces may remain free from the gynoecial strands beneath the locules, but, upon their upward course, typically come in close association with the strands until they turn outward into the bases of the sepals. Frequent branching occurs between the sepal supplies and both the peripheral small bundles of the outer ovary wall and the outer bundles of the gynoecial strands. The vascular supply to each sepal originates as three traces. Those to each sepal typically retain their identity as they slope beneath the locular area. Upon their upward course, the sepal traces branch and, along with branching of the peripheral bundles as well as the outer bundles of each gynoecial strand, increase the vasculature of the outer ovary wall.
In the constricted region, below the point of sepal attachment, many of the small bundles which constitute the outer wall vasculature slope tangentially and horizontally. These bundles anastomose with similar ones to form approximately 12‑15 larger prominent bundles, which supply each sepal. These bundles, along with the smaller more peripheral bundles in the outer ovary wall which supply the spines, form the three‑dimensional vasculature of the sepals as described by Heinsbroek & Van Heel (1969) for V. amazonica. The many bundles which enter the base of each sepal constitute the central and marginal bundle system (their terminology). Also noted by the above writers, and earlier by Knoch (1899), was the presence of both adaxial and abaxial peripheral bundle systems, found not only in the sepals, but also in the other appendicular organs (i.e. petals, stamens and staminodia). These peripheral bundle systems are fundamentally formed as a result of ramifications of the major bundles (e.g. central and marginal bundles) at the point of sepal insertion or slightly below. In the sepal, the abaxial peripheral system is formed not only by ramifications of the major bundles, but also by the continuation of the small bundles in the outermost part of the ovary wall. The bundles which contribute to this abaxial system are typically normally orientated; however, rotation of up to 900 is not uncommon. The adaxial peripheral system, as well as the abaxial system, is commonly not well differentiated. In comparison, however, the adaxial system consists of variously orientated bundles. In this system it is common to find bundles rotated by 90ºor frequently 180º from normal orientation. This aspect of orientation will be amplified in conjunction with stamen vasculature.
In transverse sections it can be seen that the appendicular organs are arranged, at least partially, in several slightly sloping helices. Some of the organs are arranged along orthostichies (Plate 4). The orthostichies do not, however, continue around the entire flower for they are intercepted by contact parastichies. Both clockwise and counter‑clockwise parastichies are discernible. In cleared and sectioned material, it can be observed that those floral organs which occur in the same orthostichy, or nearly so, receive their supplies, generally, from the same gynoecial strand(s).
The vascular supply to each of the remaining appendicular organs (i.e. petals, staminodia and stamens) is basically similar throughout the flower. Initially, the supply to each organ originates as two normally orientated, collateral traces, which lie along the same radius. The more centrifugal trace arises by a tangential division from the outer bundle of each gynoecial strand. The second trace also originates by a tangential division but, in this instance, from the inner bundle of the gynoecial strand. This pattern is reminiscent of the patterns found in Nymphaea (Moseley, 1961) and in certain distal stamens in Nuphar (Moseley, 1965). No gaps in the outer bundle of the gynoecial strands, however, such as those found in Nymphaea, are discernible. These may have been erased through condensation. The two traces which supply each of the above floral organs continue as two bundles to the base of the organ, where each trace typically branches, resulting in the formation of one median and two lateral veins. Once branched, the comparable veins may or may not fuse. This is the basic pattern found in both V. amazonica and V. cruziana. Not uncommonly, however, one of the two veins does not branch but rather fuses with the median vein produced by the other trace. It is this latter pattern, or perhaps the close proximity of the two traces, which led Moseley (1958) to consider that each of the stamens and staminodia receives a single vascular supply. Likewise, it is most probable that the basal ramification which results in the formation of a median and two lateral bundles led Heinsbroek & Van Heel (1969) to consider them to be three traces. It should also be pointed out that the larger outermost staminodia and petals, especially in V. cruziana and less so in V. amazonica, typically receive additional bundles which contribute to the lateral system of each organ. These laterals arise independently of the ones mentioned above. In contrast, they commonly arise tangentially from the outer bundle or an adjacent gynoecial strand.
The petal, staminal and staminodial anatomy of Victoria has been described by Knoch (1899) and more recently by Moseley (1958) and Heinsbroek & Van Heel (1969). Repetition of their descriptions would be superfluous here, but it is interesting to note that both Knoch and Heinsbroek & Van Heel described the peripheral bundle systems as similar to those which appear in the sepals. The adaxial peripheral system is of interest here for its role in the formation of the inverted median auxiliary vein. Moseley described the formation of this vein as the result of fusion and rotation of two lateral veins (of the central system) or their branches which are impeded by the presence of the pollen sacs. Heinsbroek & Van Heel (1969) concluded that the auxiliary vein is nothing more than the continuation of the adaxial veins which are not impeded by the pollen sacs. This observation, along with those of Knoch (1899) (who described the presence of peripheral bundles and indicated that two adaxial bundles, each lateral to an adaxial median bundle, anastomoses at the base of the connective with the median bundle and continues their course upward), agrees with the observations of this writer. He, however, agrees with Moseley (1958) that the presence of the auxiliary vein is relatively insignificant. Observations of many stamens and staminodia reveal that the inverted vein is common but that it certainly is not a constant feature of these organs. In fact, while many of the adaxial peripheral bundles do indeed have inverted bundles, this feature again is not constant in comparable organs. Finally, all the staminal and staminodial vasculatures have their origin from the ramifications which occur at the base of each organ. It is at this point that bundle rotation is a common feature.
In all flowers of Victoria examined, a well‑developed residual stele was found to be present (Fig. 1). This residual stele is principally a continuation of those vascular bundles which constitute the central vascular system of the peduncle (Plate 3C). In addition, but infrequently, smaller vascular bundles derived from the upper, inner portion of the receptacular plexus may anastomose with these former bundles and contribute to the formation of the residual stelar supply. The five or more prominent vascular bundles of the peduncle central system, which form the residual stele, represent coalesced bundles, each consisting of a central core of xylem with two or more surrounding phloem strands, a condition that is the result of anastomosing Of the bundles of the central peduncular system, as was noted earlier. Above the receptacular plexus, these bundles ramify to form several typically normally orientated, but diffuse, vascular bundles which extend upward into the projecting floral axis (Fig. 1, Plate 4A).
Surrounding the residual stele and anastomosing with it, or with branches of it, is another bundle system. This system, in view of its observed pathway, position and bundle orientation, represents the ventral carpellary supplies. The origin of the ventral carpellary supplies was similar in all the specimens of Victoria that were examined. They arise from the inner bundle of each gynoecial strand. In contrast to the position found in many of the species of Nymphaea, where the ventral supplies, which are also derived from the inner bundles of the gynoecial strands, arise beneath the locules midway between the plexus and the outer locular periphery, the ventrals in Victoria originate immediately adjacent (centrifugally) to the receptacular plexus (Fig. 1). Since, at this position, the number of gynoecial strands is smaller than the number of locules, the number of ventral carpellary supplies is also smaller than the number of locules. If, however, these latter bundles are followed upward, branching occurs in such a manner that they give rise to the same number of ventral carpellary bundles as there are locules. This point should not be confused. From their point of origin, the two ventral bundles to each carpel are fused. That these are ventral carpellary bundles is demonstrated by their‑bundle orientation. Each bundle is rotated by 90' from normal orientation and, since the two ventrals to each carpel are fused proximally, one finds several bundles in which the xylem portions have become congenitally fused.
Initially, the fused ventrals curve centripetally upward and parallel, to a degree, to the outline of the locular regions (Fig. 1). As noted, upon their upward path, these bundles ramify to increase the number of ventral carpellary bundles, and also anastomose with branches of the residual stelar tissue (Fig. 1). In addition, branches arise from the fused ventrals which supply the inner, more centripetal portions of the locular septa (Fig. 1). These branches are in turn fused but separate soon upon departure from their point of origin. As the branches separate and supply the septum, each bundle usually becomes partially inverted. Normally orientated bundles, however, occur and bundles with intermediate orientations are common. Whether these latter bundles are bundles derived from the residual stele or are branches of the ventral carpellary bundles is difficult to determine. That the partially inverted bundles are branches of the ventral carpellary bundle is unquestionable. The more normally orientated bundles are perhaps better interpreted as branches from the residual stele. This relationship most probably indicates a long association of these two vascular systems, the latter system perhaps responding to the functional requirements of the organism.
At a point midway between the receptacular plexus and the stigmatic surface (Fig. 1), or perhaps at a point slightly more distal to this, two ventral veins to each carpel become clearly recognizable. It is at this point, then, that the ventrals are no longer fused. For each carpel, these two veins are each free from the other and rotated by 90' from the normal. These ventral carpellary bundles traverse the ventral carpellary region and, upon doing so, like the dorsal carpellary bundles, form a distinct supernumerary system. Branches of this system, along with those branches of the residual stelar supply and/or the fused ventral system, supply the corresponding septal regions. In addition, supernumerary bundles may be found just below the stigmatic surfaces.
The ventral veins below the stylar processes are occasionally joined by branches from the inner bundle of a gynoecial vascular strand. These branches may fuse with the ventral bundles; but, more commonly, they remain in only close association. These veins, along with the ventral veins, branch, with each branch terminating in a stylar process (Fig. 1).