Monstera tenuis (Araceae), formerly Monstera gigantea, is a common Neotropical hemiepiphytic vine with a distinctive leaf morphology. Juveniles of Monstera tenuis are usually found in forest understory where light levels are very low, light is predominantly diffuse, and leaves are usually displayed horizontally (Oberbauer 1998). Seedlings of M. tenuis are skototropic, meaning they grow toward darkness or toward shade. The seedlings can grow up to 2 m on seed reserves before finding a host. The seedling will die if it does not find a suitable host before running out of reserves, so it must grow directly towards a host (Ray, 1983). M. tenuis host trees often share particular characteristics. Wider trees are more likely to harbor M. tenuis than random trees, as are trees with buttresses, because they cast larger shadows (Strong and Ray, 1975). Studies have suggested that M. tenuis can use skototropism to make a choice in the host tree that it selects, but other studies have suggested that there is not in fact a correlation with the characteristics of the trees but rather just an association with the detection of shade. M. tenuis has terminal flowering, and the spadix consists of perfect flowers. M. tenuis is pollinated by bees and dispersed by birds.
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).
There are three main types of calcium oxalate crystal in monocotyledons: raphides, styloids and druses. Araceae is the only family in which all three main crystal types are recorded. Calcium oxalate presence in plants can have different functions such as potential storage forms of calcium and oxalic acid or even acting as simple depositories for metabolic wastes which would otherwise be toxic to the cells or tissues. In some plants they have more specialist functions, such as promoting air space formation in aquatic plants, or helping to prevent herbivory. The barbed and grooved shape of raphides of some Araceae (e.g. Xanthosoma sagittifolium) are particularly irritating to mouth and throat tissues when eaten (Prychid and Rudall 1999).
M. tenuis has a simple alternate leaf arrangement usually displayed horizontally. Studies have shown that 75% more carbon could be gained if leaves were horizontal instead of vertical. Because the vertical leaf orientation reduces light interception, other selective factors are likely of greater importance in favoring the evolution of the shingle-leaved growth form (Oberbauer 1998). Upon reaching a tree, the seedlings begin to produce small round leaves approximately 2cm in diameter that are pressed flat against the trunk of the host tree and cover the stem. Young stems are green and presumably photosynthetic; with time they may turn brown. With leaf production comes a shortening of the internodes, (a segment of a stem between two nodes) and the stem begins to thicken. The most notable features of the older stems are the leaf scars, the axillary buds, and the adventitious roots (Madison 1977). Stems are usually flattened front to back and the portion facing the trunk produces the adventitious roots. As the stem climbs the tree the successive leaves are of increasing size. A dramatic change in leaf form occurs where the leaves develop clefts and become pinnatifid, a similar appearance to fern fronds. These leaves are held away from the trunk by the petiole and continue to increase in size and change in form until they reach a length up to 125cm. At this stage the petiole will be up to 60cm long and the stem diameter can be up to 8cm. If the stem reaches the top of the tree, it is still capable of returning to the ground. This requires a change in the stems form involving an elongation of the internode and a reduction of the stems diameter and leaf size.
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.
M. tenuis is found in the neotropical lowlands of moist tropical forests throughout Central America. The center of diversity for this species is from Southeastern Nicaragua to Western Panama where it is native (Gargiullo et al. 2008).
