DEVELOPMENTAL STUDIES IN PTYCHOSPERMA (PALMAE). II. THE STAMINATE AND PISTILLATE FLOWERS

The staminate flower of Ptychospercma mooreanum and P. gracile has three imbricate sepals, three valvate petals, an androecium of 9-13 or 27-32 stamens, and a lageniform pistillode. Pistillate flowers have three imbricate sepals, but the three petals are also imbricate, and the three (-seven) staminodes are irregular and sometimes basally fused. The ovoid pseudomonomerous pistil has a single locule with a pendulous ovule and three small distal stigmatic lobes. All floral organs are initiated by periclinal divisions in the second tunica layer of the floral apex, with divisions in the outer layer of the cortex also apparent in the initiation of stamens and staminodes. Primordia of floral organs differ in shape but can be related to those of other palm flowers. Sepals are initiated and develop successively, and during floral organogenesis are horizontally oriented covering other organs. Petals are also initiated successively, but rapidly attain equal size. Petals of staminate and pistillate flowers are initially similar, but subsequent prolonged activity of marginal meristems results in widely imbricate petals in pistillate flowers. The polyandric androecia are clearly trimerous. As stamen initiation commences, the apex is divided into sectors or primary primordia consisting of a narrow ridge opposite each sepal and a large triangular bulge opposite each petal. Stamens arise as secondary primordia in alternating antesepalous and antepetalous cycles. Variation in number of stamens is due primarily to variation in the number of primordia that arise in the wider lower antepetalous loci. The primordium of the pistillode is girdling but becomes trilobed later. The gynoecium is initiated as three unequal crescentic carpel primordia that are united by zonal growth early in development. A procambial strand develops acropetally into each floral organ, and additional strands are formed as each organ increases in size. Floral organs are histologically specialized. The appearance of tannins, raphides, and silica and the maturation of sclerenchyma are basipetal within each floral organ. THE USEFULNESS of ontogenetic studies in elucidating the mechanisms of morphological change has been pointed out by Kaplan (1971). Recent work has further emphasized the value of developmental studies in analyses of flower structure. In the monocotyledons, the multiparted flowers of Alismatales, long considered spiral in organization, have been found to be basically trimerous (Singh and Sattler, 1972, 1973, 1974). Other work (Hiepko, 1964; Leins, 1964; Kania, 1973) has indicated that polyandry may be secondary in some dicotyledons. The original goal of this paper was to obtain information on the development of multistaminate androecia for a survey of androecial structure within the palms. The study has also yielded information on the evolution of dimorphic perianths, staminodes, a lageniform pistillode, and a pseudomonomerous gynoecium. Various histological features of the flowers can 1 Received for publication 11 December 1974. This work was supported by NFS grant GB-37680X to Harold E. Moore, Jr. The author thanks Dr. R. Sattler for valuable discussions, and F. B. Essig, L. Klotz, and Dr. M. V. Parthasarathy for reading the manuscript critically. Figures 1-10 were prepared by M. R. Sheehan and technical assistance was provided by J. Kaltaler. be related to phenology and other factors in pollination (Essig, 1973; Uhl and Moore, 1973). MATERIALS AND METHODS-Material and methods are the same as those described in the previous paper (Uhl, 1976), but certain aspects of the floral material should be noted. The three flowers of each triad develop in sequence (Uhl, 1976). The inception of floral organs reflects the age of each flower, as may be seen in Fig. 11 where the first staminate flower has three sepals and only one sepal is developed on the second staminate flower. The subtending bracteole and apex of the pistillate flower are present, but are concealed by the large keel of the second sepal (2se) of the first staminate flower. The developmental lag in the three flowers of a triad may also be noted in Fig. 21. Because of the differences in age of the two staminate flowers of each triad, more stages of staminate than of pistillate development were available. In any inflorescence all equivalent flowers are at exactly the same stage. The precision is such that cell divisions initiating the same floral organ could be seen in all similar flowers within an inflorescence. Flowers of both Ptychosperma mooreanum F. B. Essig (LAE 55066)