Monographs Details: Stenopadus
Authority: Carlquist, Sherwin. 1957. Anatomy of Guayana Mutisieae. Mem. New York Bot. Gard. 9 (3): 441-476.
Scientific Name:Stenopadus
Discussion:This genus demonstrates the most elaborate floral venation yet found in Compositae. A basic but by no means typical situation is found in Stenopadus campestris (fig. 102). In the corolla of this species (fig. 102A), a pair of lateral veins is found in each lobe. These extend from the tips of the lobes to the base of the corolla; adjacent laterals fuse in the achene top, not in the corolla itself. Occasionally (fig. 102 C, extreme right), adjacent laterals do not fuse but remain separate in the achene. In addition to the laterals, median veins are present in each lobe. Median veins extend for various distances into the corolla lobes. If they do not extend to the tip, they terminate freely, as do the laterals; if they do extend to the tip, they join with one of the laterals at the tip. Median bundles extend into the achene, where they continue as five of the exterior bundles (fig. 102 C). The xylem of stamen traces terminates freely in the top of the achene or joins with that of corolla bundles. In details of venation, the corolla of 5". campestris resembles that found in Fitchia speciosa of the Keliantheae (Carlquist 1957b). The style of S. campestris (fig. 1 B) is vascularized by a pair of dorsiventrally arranged bundles; these continue into the achene (fig. 102 D), joining two of the exterior bundles on opposite sides of the achene base. In addition, numerous other interior bundles are present in the achene. At the achene base, a lateral pair of these join with the ovule trace for a short distance (fig. 102 H), separating below to join exterior bundles, as do the remainder of the interior bundles (fig. 102 I). Thus, there are approximately ten bundles arranged in a cylinder passing from the achene base into the receptacle. The ovule trace (fig. 102 D, G) branches dichotomously in the chalaza, and the adaxial portion is double.

A somewhat more complex situation is represented by Stenopadus kunhardtii (fig. 103). In the corolla (fig. 103 A), lateral and median veins are present, as in S. campestris. In addition, subsidiary veins branch from the laterals at various points between the level of departure of stamen traces and the bases of the sinuses. These subsidiary veins occupy a position between the lateral veins and the margins of each lobe, and extend for various distances into the distal portion of the lobes, where they terminate freely. This pattern of corolla venation has been found elsewhere in the Compositae only in Fitcbia mangarevensis (Carlquist 1957 a, b). At the base of the corolla of S. kunhardtii, the laterals continue into the achene, without fusion of adjacent laterals (fig. 103 C). Likewise, the five median veins of the corolla extend into the achene independently. The xylem of stamen traces terminates freely in the achene top. In the achene, more than the fifteen bundles continuous with those of the corolla are found. These additional exterior bundles (fig. 103 Qare branches of the fifteen corolla bundles. As in S. campestris, the style of S. kunhardtii contains two bundles (fig. 103 B) which connect with a dorsiventrally arranged pair of bundles in the achene (fig. 103 D). These connect with adjacent exterior bundles in the achene base (see also fig. 103 I, J). Numerous other interior bundles are present in the achene. These terminate freely above, but connect in a plexus with the ovule trace below, this plexus then separating to join several of the exterior bundles in the achene base (fig. 103 I)- The ovule trace (seen also in fig. 103 G) is branched several times. At the base of the achene, a cylinder of bundles enters the receptacle.

In Stenopadus stipitatus (fig. 104), as in S. kunhardtii, there is a remarkably complex corolla vasculation(fig. 104 A). Because of the various ways in which the bundles unite, the designation of median, lateral, and subsidiary bundles cannot be made in S. stipitatus. The basic pattern of five bundles in each corollalobe seems evident, however. All bundles of the corolla-lobes terminate freely above. At the corolla base, as in S. kunhardtii, the bundles in the corolla tube pass into the achene without union of adjacent laterals (fig. 104 C). Xylem of most stamen traces terminates freely in the achene summit without coming in contact with that of the corolline bundles. As in the two above species, two style bundles are present (fig. 104 B, C, E). These are connected with a dorsiventral pair of interior achene bundles (fig. 104 D). In addition, a lateral pair of interior bundles is present; all four interior bundles, together with the ovule trace, form a vascular plexus at the achene base (fig. 104 H). This separates, further down, to form strands joining the exterior bundles (fig. 104 I). The ovule trace is dichotomous on the adaxial face of the ovule (fig. 104 G). As in the above species, a cylinder of bundles enters receptacular tissue.

In Stenopadus cucullatus (fig. 105), a much simpler corolla venation is found (fig. 105 A). Lateral bundles, which fuse at the apex of each corolla lobe, are present, but median veins are only occasionally present in lobes, and do not extend into the tubular portion of the corolla. As in S. kunhardtii and S. stipitatus, the lateral bundles enter the achene, without union of adjacent laterals, and form a series of external bundles (fig. 105 C). In the style (fig. 105 B), a pair of larger dorsiventrally arranged bundles is present; in addition, a lateral pair of small bundles extends part way up the style, fusing with the larger bundles.

The four style bundles extend from the style into the achene (fig. 105 D) where they become interior bundles (fig. 105 F). The two lateral interior bundles branch in the lower half of the achene (fig. 105 G) so that they are double along part of their extent. The dorsiventral pair of interior bundles connect, at the achene base, with adjacent exterior bundles. The lateral interior bundles, together with the ovule trace, form a plexus (fig. 105 H) which separates lower down (fig. 105 I) to join exterior bundles. A cylinder of bundles connects with receptacle vascular tissue. The ovule trace is dichotomously branched (fig. 105 D, G). For comparison, an ovule trace of 5. chimantensis is shown in figure 105 J- In the ovule studied of this species, the trace was dual in two places, although single at the base and at the chalaza.

Among the other species of Stenopadus for which material was available, S. chimantensis, S. connellii, S. huachamacari, S. obconicus, and S. sericeus were found to have corolla vasculation like that of S. cucullatus, though median bundles were entirely lacking in these species. Median bundles were found in the lobes, though not in the tube, of S. colombianus corollas. Two bundles were found in the styles of all of these species, and various numbers (though not fewer than four) interior bundles occurred in the achenes. Ovule traces may or may not be branched in these species. The frequency within the genus of various vascular conditions could not be ascertained from the material available. It is sufficient for the purposes of the present study, however, to note that certain conditions seemingly not present in the majority of mutisioids are prominently represented in Stenopadus. These features may be summarized as follows; median veins are present in the corolla in addition to lateral bundles (which branch to form subsidiary bundles in some species); the lateral bundles are not united in the corolla, and may or may not be united in the achene; xylem of stamen traces often terminates freely in the summit of the achene; at least 10 exterior bundles are present in the achene; two, sometimes four, style bundles continue into the achene as interior achene bundles; a dorsiventral pair of interior bundles is always present, and two to several lateral interior bundles are present in the achene; characteristic vascular configurations occur at the base of the achene, in all species forming a cylinder of independent bundles which enter receptacular tissue; the ovule trace is often dichotomously branched, though it may be further ramified or unbranched.