Protection of Developing Seeds in Neotropical Araceae

PROTECTION OF DEVELOPING SEEDS IN NEOTROPICAL ARACEAE MICHAEL MADISON The Marie Selby Botanical Gardens, 800 S. Palm Ave., Sarasota, FL 33577 In flowering plants with ani When the fruit ripens mechanisms mal pollination and seed dispersal of attraction come into play once the reproductive cycle can be con more, including softening of the sidered to consist of four stages, re pericarp and production of colors presenting alternating phases of and fragrances. In a number of tro protection and display. In the pro pical genera, (e.g. Codonanthe, He tective phases immature flowers dychium, Marcgravia, Pittosporum, and fruits are safeguarded from Cariudovica, My ristica ) the pericarp predation and parasitism, while in breaks apart at maturity to reveal the display phases pollinators and the seeds with brightly colored arils dispersal vectors are attracted. or embedded in a juicy, colored pla This alternation of protection centa. and display is accomplished by a Since the adaptations for pro variety of mechanisms. Initially the tection of immature structures are developing flowers are protected by often contrary to the requirements bud scales, stipules, bracts, or the of the attractant phases, a delicate calyx and by cryptic coloration. As ly attuned sequence of developmen the flowers mature bud scales or tal events is required. Most studies stipules abscise and the pedicels or of reproductive biology have dealt peduncles elongate, elevating the exclusively with the attractive flowers to an exposed position. phases rather than considering the Heat, floral fragrances, and con cycle as a whole (e.g. Ridley 1930, spicuously colored bracts, perianth, van der Pijl 1969, Faegri and van or stamens may be elaborated; the der Pijl 1966, Proctor and Yeo effect of these in attracting pollina 1973), even though the adaptations tors may be enhanced by simultan of flowering plants to the protec eous deciduousness of the plant. tive phases are diverse and worthy Nectar or abundant pollen may be of study. A notable exception is the additional attractive factors. Fol investigations of Uhl and Moore lowing pollination is a second cryp (1973, 1977) which constitute a tic phase during which the develop superb study of protective mechan ing fruit is protected by abscision isms in the reproductive structures of showy perianth parts, by rapid of palms. formation of a hard pericarp, often In this paper I report observa cryptically colored, by accretion of tions on the reproductive cycles of the calyx or bracts, and/or by ela neotropical species of the family boration of chemical defenses. Araceae (philodendron family), 52 1979] MADISON: SEED PROTECTION 53 with special attention to the protec leaf-like, and in many species it tion of immature seeds. This fami serves only to protect the develop ly, with about 30 genera and 1200 ing spadix, becoming reflexed as species in the neotropics, forms a the spathe matures (Figure 1). conspicuous element of the vegeta However in some species, e.g. A. an tion in wet regions and includes dreanum, it is broad and brightly aquatics, terrestrial herbs, lianas colored and apparently plays a role and epiphytes. Except for a few re in pollination. In a group of species marks by Engler (1920) and Ridley allied to A. pedatum the spathe is (1930) hardly anything has been shaped like an inverted canoe with written about the fruits of aroids. the spadix pendent below (Figure The descriptions which follow are 2); in this case the spathe has ac based on observations of plants in quired the function of an unbrella. the wild made in the course of These species are native to very wet studies carried out since 1971 in middle elevation forests of the Central America and the Andes. western slopes of the Andes where One of the defining features there is a high probability of rain of the aroid family is the structure disturbing nectar or pollen. I have of the inflorescence, which consists observed Anthurium c.f. gualea of a spike of tiny flowers, termed num in Ecuador during a heavy the spadix, subtended by a large rain; the spadix, which was at an colored bract, the spathe. In all spe thesis, remained dry and was visited cies the spadix is protected before by flies, weevils, staphylinids, and anthesis by being tightly wrapped other insects. in the spathe, an additional layer of With the exception of the ge covering is provided by the sheath nus Spathicarga floral nectaries ing base of the subtending leaf or have not been reported for the Ara cataphyll. The initial phase comes ceae. However, copious production to an end with rapid elongation of by the pistils of stigmatic fluid, the peduncle and unfurling of the which is often, sweet to the taste, spathe to expose the spadix. From may to some · extent compensate this point a great diversity of flower for this deficiency. In Anthurium ing and fruiting mechanisms come stigmatic fluid is often abundantly into play, which are here described produced, and each flower elabor for each genus arranged according ates about the same amount (in to the subfamilial and generic classi contrast to Monstera where some fication of Engler (1920). flowers specialize as stigmatic fluid exuders). POTHOII)EAE The developing fruit in An thurium is protected by the cucul Anthurium: Anthurium in late tepals which almost entirely cludes about 600 species of terres cover it (Figures 3, 4). A layer of trial herbs, climbers, and epiphytes. sclereids below the epidermis pro The flowers are perfect and have vides a mechanical barrier around four tepals in two whorls of two; the berry. As the spadix ripens the the chief pollinators are flies, sphe berries soften and swell, and appar cid wasps, and the male euglossine ently increasing pressure in the spa bees. The spathe is usually flat and dix causes the berries, which abscise 54 AROIDEANA [Vol. 2 from the axis, to 'pop out' from bose or boat-shaped; the flowers are among the tepals (Figure 5). The perfect and lack a perianth, and are berries do not fall to the ground, pollinated by Trigona or related however, but dangle on four threads bees. Though nectaries are absent, representing part of the epidermis the basal flowers on the spadix are of the inner two tepals. These dang usually sterile and produce copious ling, brightly-colored berries, remi sweet stigmatic drops, apparently niscent of Magnolia seeds, are dis functioning as nectaries. persed by birds, as sometimes noted Since the perianth found in on herbarium specimens. Analysis Anthurium is lacking, the develop of stomach contents of Manacus ing seeds are protected by a differ manacus in western Ecuador showed ent mechanism. The stylar portion the birds to have been feeding heav of each ovary contains numerous ily on berries of Anthurium doli needle-like trichosclereids, all lying chostachyum (personal communi parallel to the axis of the flower cation from C. H. Dodson). (Figure 9). These tough needles, In some cases the popping out 1-2 mm long, form a considerable of the berries exposes a previously mechanical barrier around the de hidden bright color. For example, veloping seeds. At the time of ma in Anthurium buenaventurae the turity the fruit breaks in two trans developing spadix is dark purple, versely and the needle-bearing up including the tepals and protuber per portion falls away, reavealing ant apices of the berries. As the ber the seeds in a gray or brightly co ries are squeezed out from among lored pulp (Figure 10). The seeds the tepals the lower portion, which are picked off by birds. is bright yellow, becomes exposed, In Monstera punctulata the apparently signalling to dispersers protection of developing seeds pro that the fruits are ripe. vided by the trichosclereids is Heteropsis: I have observed augmented by a tough cap of iso fruits only of Heteropsis integerri diametric sclereids lying just below ma. The spathe abscises even before the epidermis of the ovary. Mon anthesis and the white spadix is stera obliqua lacks sclereids in the visited by bees and small hemiptera. fruit altogether, and also lacks the The developing fruit is green and abscission layer to discard the up the seeds are protected by a hard, per portion. This species has fruits sclerified pericarp. At maturity the which mature in only 6-8 weeks, pericarp softens and turns orange. while fruits of other species requrie The'musty-smelling fruits are borne up to 15 months (Madison 1977). at the ends of elongate hanging The lack of any apparent mechan branches, a situation suggestive of ism for protection of immature bat dispersal. fruits may be related to rapid ma turation. MONSTEROIDEAE Stenospermation: This genus Monstera; Monstera includes includes about 30 species of true about 25 species of scandent epi epiphytes with short stems and phytes, many of which have natur leathery leaves. The. floral structure ally perforated leaves. The spathe is very similar to that of Monstera, is white, yellow, or pink, and glo- and the globose spathe is deciduous 1979] MADISON: SEED PROTECTION 55 after anthesis. The developing seeds to the ground. This species is most are protected by needle-like tricho abundant along waterways, and sclereids in the apical region of the since the seeds float many of them ovary. At maturity the fruits turn may be water-dispersed (Bunting, yellow or orange and become soft. 1960). In addition, the swollen and The trichosclereids are not shed in juicy funiculus remains attached to a deciduous cap, as in Mons te ra, the seed, and this may serve as an but remain in the mature infructes elaiosome in dispersal by ants cence, which is pecked apart by which would find the seeds lying on birds or consumed by insects.

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