Floral Development in Aphandra (Arecaceae)1

American Journal of Botany 88(2): 185–195. 2001. FLORAL DEVELOPMENT IN APHANDRA (ARECACEAE)1 ANDERS S. BARFOD AND NATALIE W. UHL2 Department of Systematic Botany, Aarhus University, Nordlandsvej 68, DK-8240 Risskov, Denmark; and L. H. Bailey Hortorium, 467 Mann Library, Cornell University, Ithaca, New York 14853 USA The organogenesis of staminate flower clusters and flowers and some observations on the corresponding pistillate structures of Aphandra natalia are described and compared with those of the other two genera in the Phytelephantoideae (Arecaceae). In Aphandra, staminate flowers are borne in monopodial clusters of mostly four (1–6) flowers. Each flower is surrounded by two pairs of subopposite bracteoles and has two rather indistinctly four-parted whorls of perianth parts. Stamen primordia arise on a shallow apical dome and then centrifugally down the sides of a long, angled, and laterally flattened receptacle. Immediately before the staminate bud opens, the floral receptacle below the androecium rapidly elongates, becoming funnel-shaped, with the bracteoles and a perianth sheath adnate to it forming a pseudopedicel. Epidermal and subepidermal layers of these pseudopedicels split at anthesis and release a great number of raphide idioblasts that resemble the pollen grains in shape and size. It is hypothesized that the idioblasts deter pollen feeding or ovidepositing insects. The phylogenetic implications of these findings are important within the Phytelephantoideae and among palms in general. Key words: Arecaceae; Aphandra natalia; floral development; monotocotyledons; palms; Phytelephantoideae; pollination; pseudopedicel. Aphandra natalia (Balslev and Henderson) Barfod is a pin- ficult to obtain since large valuable trees must be felled to get a series. Inflo- nate leaved, single-stemmed palm found in Amazonian Ec- rescence stages were obtained from three individuals growing in semi-culti- uador and Peru near the foothills of the Andes. The genus vated populations near Logronõ, Province of Morona-Santiago in Ecuador, the belongs to the subfamily Phytelephantoideae, which includes type locality of Aphandra natalia. The young inflorescences (Figs. 1–4) (Ta- only three small genera and constitutes a morphologically iso- ble 2) were fixed in FAA (formalin-acetic acid-alcohol) in the field and after lated group of dioecious genera within the Palmae (Uhl and 2 d, transferred to storage in nine parts 70% glycerine alcohol to one part Dransfield, 1987). Developmental studies have shown that the 10% glycerine. Prophylls and peduncular bracts (PD bracts) were cut open to phytelephantoid genera have the only monopodial flower clus- facilitate infiltration. ters in the family, a four-parted perianth otherwise known only in only one species of Chelyocarpus (Coryphoideae), and cen- Scanning electron microscopy—The various pistillate and staminate de- trifugal stamen inception. Partial centrifugal stamen develop- velopmental stages were critical point dried in a Biorad CPD-750 Apparatus, ment is known to occur elsewhere only in the genus Eugeis- mounted on stubs with double-adhesive tape, and coated with platinum in an sona (Calamoideae) (Uhl and Moore, 1977; Uhl and Drans- Edwards S150B Sputter Coater. They were studied with a JEOL 840 Scanning Microscope at 20 kV. field, 1984). Balslev and Henderson (1987) originally referred Aphandra natalia to Ammandra based on the prominent submarginal Clearings—Material for study of vasculature was cleared using a 5% solution of NaOH and left overnight in an oven at 50ЊC. After 24 h the NaOH veins on the pinnae and the pedicellate condition of the sta- was changed and we repeated the procedure until clearing was satisfactory. minate flower clusters. Monographic work on the subfamily The material was then rinsed in distilled water and treated with commercial Phytelephantoideae has shown that it is a distinct genus (Bar- bleach to remove any cloudiness. Subsequently preparations were stored in fod, Henderson, and Balslev, 1987; Barfod, 1991) (Table 1) glycerine alcohol. The material was stained in a basic fuchsin solution (1 g and that the structure of the floral pedicel is critical. Devel- of fuchsin and 6 g of solid KOH in 100 mL water) for photographing. opmental studies of the inflorescence and flowers of Aphandra are important for eludication of the pedicel and for comparison RESULTS with developmental patterns previously described for the other genera of Phytelephantoideae (Uhl and Moore, 1977; Uhl and Inflorescence structure—In wild populations of Aphandra Dransfield, 1984). In this study we address three issues in par- natalia the distribution of staminate and pistillate individuals ticular: ontogeny of the staminate flower cluster, stamen in- is almost even. Flowering occurs throughout the year, peaking ception, and the structure of the pedicel of the staminate flow- slightly in February–March (Barfod, 1991). Inflorescences er. Some observations are also presented on the development form in acropetal sequence in the axils of their subtending of the pistillate flower clusters and flowers. leaves. All leaves produced during periods of flowering subtend a young inflorescence bud. The pistillate and staminate MATERIALS AND METHODS buds have a similar overall appearance while they are still included in the sheaths of the subtending leaves, but they de- Plant material—Aphandra is exploited for fibers extracted from the leaf velop differently after the peduncular bract (PD bract) breaks bases (Borgtoft Pedersen and Balslev, 1990); developmental material is dif- through the prophyll (Figs. 1–7). In the staminate bud, the PD bract continues to grow and before it splits will attain more 1 Manuscript received 21 December, 1999; revision accepted 27 April 2000. The authors thank Anni Sloth for assistance with laboratory work, SEM, than twice the size of the prophyll. At anthesis the entire in- and electronic processing of the photographs; and the reviewers. Support is florescence is exposed and pendant. The pistillate bud, in con- acknowledged from NSF grant BSR-8806042 to NWU. trast, elongates only a little after the splitting of the prophyll, 2 Author for correspondence (e-mail: [email protected]). the PD bract reaching only about three-quarters the length of 185 186 AMERICAN JOURNAL OF BOTANY [Vol. 88 TABLE 1. Diagnostic table. Ammandra decasperma Aphrandra natalia Phytelephas macrocarpa Phytelephas aequatorialis Pistillate inflorescence No. of flowers per inflorescence 6–10 30–50 5–25 15–25 No. of sepaloid bracts 0? 4–6 4–6 4–6 No. of perianth segments 7–10 7–9 5–8 6–9 No. of carpels 6–9 6–8 4–5 5–6 Staminate inflorescence Length of rachis 30–60 100–170 30–60 90–150 Axis of flower cluster at anthes- present indistinguishable indistinguishable indistinguishable isa No. of flowers per cluster b 6–9 4 (Ϫ5) 4 (Ϫ5) 4 (Ϫ5) Pedicel pseudopedicel?c pseudopedicelc indistinguishable pedicel Distribution of idioblasts concentrated in even even even blisters Idioblast released at anthesis yes yes no no No. of sepaloid bracts 0? 4 4 4 No. of perianth segments 8? 8 8 8 Shape of male receptacle at an- elongated, recurved elongated, dome flat to dome shaped widened, flat thesis shaped Stamen inception centrifugal? centrifugal, sequential centrifugal, sequential centrifugal, in 2 phases No. of stamens 300–500 400–650 150–300 500–700 Length of filament at anthesis 0.1–0.2 2.5–3 3–9 6–10 Length of anthers at anthesis 0.5 3–3.5 4–6.5 3–5 Pistillode ϩ/Ϫ present absent absent absent Size and shape of pollen grain 45–55, rounded 60–70, elliptic 55–65, elliptic to 80, elongate elongate Pollen grain aperture monoporate monosulcate monosulcate monosulcate a The individual pseudopedicels or pedicels of the flowers of Aphandra natalia and Phytelephas aequatorialis are fused, thus forming a pseudo- axis. b Aberrant number in parentheses. c Pseudopedicel formed by fusion and elongation of the perianth and the receptacle (see text). the prophyll. The rachis of the pistillate inflorescence is much comes adpressed to the rachis with the posterior flower partly shorter, and the flowers remain closely bunched. At anthesis, hidden (Fig. 19A). they are partly contained in the PD bract, which splits longi- tudinally along the abaxial side to expose only the tips of long Organogenesis of staminate flower clusters and flowers— strap-shaped perianth parts and stigma branches (Fig. 19C). In the earliest developmental stages available to us, the flower cluster sites are covered by their subtending bracts. Removal Structure of the staminate flower cluster—The staminate of the bract exposes a lentil-shaped apical dome in each flower inflorescence of Aphandra natalia breaks through the PD bract cluster (Fig. 16). The two bracts that subtend the lateral flow- in the evening and finishes development overnight. Elongation ers (Fig. 16: A, B) are clearly discernible (ba and bb), whereas proceeds at up to 10 cm/h until the rachis has attained a length the subtending bracts of the posterior and anterior flowers, of 100–170 cm at anthesis the following day. The staminate respectively, are not visible in distal view. The apices of the flowers are gathered in 200–300 spirally arranged and densely four flowers are flattened to slightly dome-shaped (Fig. 17: A, inserted clusters (Figs. 6, 19A). The individual clusters have B, and D). In distal outline, they appear three- to four-lobed mostly four (1–6) flowers. Lower, stalklike parts of the flowers because of primordial bulges (Fig. 18, 19D). On the lateral are united to varying degrees and taper proximally to a com- flowers, a pair of subopposite bracteoles develops first, slightly mon attachment (Figs. 8, 19A). The basal clusters have fewer displaced relative to the plane of symmetry (Figs. 16, 19: 1b, flowers, usually two or three, and a number of solitary flowers 2b, 1a, 2a). The posterior member of this pair is usually visible are always present at the apex of the inflorescence. Each clus- before the anterior one. On the posterior flower of the cluster, ter is subtended by a bract that differs in shape and size from the first-formed pair of subopposite bracteoles can be distin- deltoid and is ϳ3 cm long at the base of the rachis to a narrow, guished in lateral positions (Fig.

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