Monstera tenuis K.Koch

Monstera is a liana of the monocotyledonous family Araceae, commonly referred to by its genus name (Ray 1983). Monstera is restricted to the Neotropics, particularly moist and wet forests from sea level to 1800m. Found mainly in the geographical range of Southeast Nicaragua to Western Panama (Gargiullo et al. 2008) with a high abundance specifically in La Selva, Costa Rica. According to Ray (1983), the seedlings of Monstera are dropped a few inches from a tree and upon germination exhibit strong, skototropic (tendency to grow towards the shade or darkness) growth towards the base of the closest tree. Until, the seedling reaches the trunk of a tree, it doesn’t produce leaves. The first leaves Monstera produces, when it does reach a tree, are very small, circular leaves with entire margins pressed flat against the trunk. As Monstera ascends into the canopy its leaves get bigger and bigger until when the successive leaves attain a diameter of about 25-30 cm, a dramatic change in leaf occurs. The leaves develop deep clefts and become pinnatifid, having the appearance of fern fronds. Mature leaves can get up to 125 cm long. These mature leaves are capable of returning to the ground, however, when they descend they do not return to their juvenile leaf morphology, but instead retain their mature form (Ray 1983). This unique developmental morphology has attracted much interest in the scientific community and has sparked a debate on possible causes for this leaf modification (Ray 1983, Zuchowski 2005). Some studies suggest that there is a threshold of available light necessary to induce morphological change. A study that tested this hypothesis found that the change in morphology occurred at a lower height in habitats with more available light and that the size of the last juvenile leaf increased with light availability (Pfitsch 1999). Meanwhile some people (Ray 1983) are skeptical of these results. Ray (1983) writes that a tree standing in an open field receives rather uniformly high isolation on the lower portion of the trunk. Yet, when M. tenuis grows on such a trunk, it does not switch to the mature leaf form at the base of the tree. Light may affect the rate at which the changes occur but it does not affect their nature (Ray 1983). Additional characteristics of Monstera include alternate leaves, aerial roots and numerous, small, white flowers on a terminal inflorescence (Gargiullo et al. 2008). These perfect flowers are on a uniform spadix with an erect, concave spathe that falls off when the flower has been successfully pollinated by bees (Zuchowski 2005). These flowers then turn into large infructescences about 30 cm long, containing about a 1,000 fruits each (Ray 1983). The fleshy, yellow fruits provide a reward for birds, which aid in dispersion of seeds. Monstera blooms and fruits most of the year (Zuchowski 2005).

A robust hemiepiphytic climber on large trees, to 30 m. tall, with an open habit of growth, juveniles are found in the understory. Juvenile: a shingle plant, the laminae nearly round. Adult stem: smooth, 6-8 cm. wide, 4-6 cm. thick, the internodes 8-12 cm. long; leaf scars are shallow, less than 2 cm. wide at the widest point, axillary bud in a depression not extended into a sulcus. Petiole: 1/3 to 1/2 the length of the lamina, 30-60 cm. long, vaginate to the lamina base, the sheath wings persistent, to 6 cm. broad near the base. Lamina: bright green, not glossy, oblong ovate, truncate at the base, the apex acute, 60-125 cm. long, 45-70 cm. wide, deeply and regularly pinnatifid, constricted near the base; primary lateral veins one per pinna, prominent and white abaxially, the secondary lateral veins are parallel to the primary. Peduncle: 10-15 cm. long, 3-4 cm. thick. Spathe: white, 20-25 cm. tall. Flowering spadix: white, cylindrical, tapering to the apex, 18-24 cm. long, 3.5-5.0 cm. thick, the pistils truncate. Fruiting spadix: green, becoming yellow at maturity, 22-35 cm. long, 5.5- 9.5 cm. thick, the seeds oblong, 10-12 mm. long (Madison 1977). 

Isotype for Monstera gigantea Engl.
Catalog Number: US 615081
Collection: Smithsonian Institution, National Museum of Natural History, Department of Botany
Verification Degree: Original publication and alleged type specimen examined
Preparation: Pressed specimen
Collector(s): A. Tonduz
Year Collected: 1899
Locality: Forets de las Vueltas, Tucurrique, Costa Rica, Central America
Microhabitat: Forest
Elevation (m): 635 to 635

M. tenuis has terminal flowering and a branch that is continued by an auxiliary shoot. During development of the continuation shoot, the inflorescence is displaced to the side and appears axillary (Madison 1977). The stem flowers and shoots as it continues to climb. The spadix consists of perfect flowers, each with four stamens and lacking a perianth, and the spathe is deciduous after anthesis (Madison 1977). Flowers are pollinated by bees and the flowers then turn into large infructescences about 30 cm long, containing about a 1,000 fruits each (Ray 1983). Monstereae are unique among the aroids in having meridiosulcate foveolate pollen (Madison 1977). The fleshy, yellow fruits provide a reward for birds, which aid in dispersion of seeds. Monstera tenuis blooms and fruits most of the year.