Tropical Morphology
How Plants Adapt to Rain Forest
Reproductive Strategies
Presentation #2 –Rain Tolerant Flowers
By Paul A. Thomas
Slide 1: Title Slide
Slide 2: About The Author
Slide 3: Learning Objectives
1. Discover that flowers exhibit many adaptations to heavy and persistent rainfall, including protective waxy layers, stiff cell structure and drip tips.
2. Be able to describe how some tropical flowers utilize water as an attractant for pollinators, and/or capture nutrients that are in drops of water passing thru the jungle canopy.
Slide 4: Rain forests form where warm, moist air, usually from an ocean area, passes over a mountain range. As the air lifts and cools, rain occurs. Thus rain forest showers are different from say, Midwestern US showers in that they can be very prolonged, sometimes lasting days. If a tropical storm passes over the mountain range, very, very intense rains can occur. The author witnessed one such day in Uvita Costa Rica where 11 inches fell in one night. Tropical flowers must be able to deal with this amount of rain fall to survive. There are two problems. One is the weight of the rain water accumulating on the flower, the second is the opportunity for plant diseases to infect the plant. Wet flowers are the perfect environment for fungi and bacteria to establish and infect the plant. Thus by allowing the flower structures to drain and dry quickly, the issues are minimized.
Slide 5: Many tropical rainforest flowers are thick stemmed, with very strong, waxy sepals and petals. They rain bounces off, or at least the force is redirected, and water is channeled off before it can weigh the flower down. The petals and sepals may be held close together until the day they open, and then close up or change configuration to again repel water. This ginger flower has reflexed lower sepals (protecting post-pollinated flowers), open sepals that support the upward facing florets that collect some water to attract pollinators, and tightly clasped sepals protecting immature flowers at the top. Pollinatible flowers are staggered. This way, a few days of bad rain won’t prevent the plant from making seed.
Slide 6: Thick waxy, protective coatings and “minimal” but stiff flower parts are another adaptation to heavy rains. There’s not much chance of water accumulation on this flower structure.
Slide7: Many species of tropical flowers employ a drip tip, or a gradually thinner tip to the sepals and petals. As water drains down the sepal/petal, there is less tissue for the water to cling to, and the smaller surface area causes the water to bunch up into heavy droplets. At some point, the droplet is too heavy for the surface tension and the droplets falls to the ground…this draining more water than if the petal or sepal had just a rounded edge.
Slide8: Several species employ a slight variation. This Heliconia presents its flowers upside down, so water drains quickly off its waxy sepals. The flowers are pollinated by hummingbirds which don’t mind the flowers being upside down. The tip of the inflorescens itself is a modified drip tip!
Slide 9: Some plants do the opposite. They take advantage of the rain water and use it to attract pollinators looking for a drink such as butterflies, hummingbirds and small jungle birds. The bird-of-paradise plant does this well, with very stiff flower stalks that can support a full cupped bract full of water. The flower is the orange and blue parts, and the blue, modified petal directs the insects and hummingbirds to the center where the pollen and the stigma ( the female part of the flowers that makes seed) is located.
Slide 10: The bromeliad has a unique way of doing this. The plant lives up in the trees (Epiphytic) and forms a rosette of leaves and bracts (the purple leaves). It forms a nest like structure that collects water. All kinds of wild life live here including tropical frog tadpoles, mosquitos and beetles. The center is always wet. The bromeliad can also adsorb nitrogen and other nutrients from the insect and animal waste, as well as whatever nutrients are collected from drops that have passed over canopy leaves.
Slide 11: This ginger shows another water collecting adaptation where every floret bract forms a cup and hold a small amount of water…just enough for one tadpole to live in! Notice how thick and stiff the stems of the flower stalk are. The flower structure can hold up to a pound of water! Look closely. Do you see the tiny flower sticking out from the water pool in the bract cup?
Slide12: Many trees and tropical vines flower at the top of the forest canopy. The sunshine is very bright and the wind allows faster drying. Because the flowers are directly exposed to driving rain, the flowers reproductive structures are protected by tubular sepals. These plants depend on long beaked hummingbirds and long-tongued moths for pollination. If water does get into the tube, the additional weight causes the flower to bend down, draining the water out.
Slide 13: Many orchids live at the top of the canopy and have similar flower adaptations. This Brassavola has tubular, moth- pollinated flowers and an extensive drip-tip system that drains water away quicky.
Slide 14: The tropical flowers on the Aristolochia vine is a bit unusual in that it has fused petals that forma one big flower structure. The big (7” wide), floppy flower dry’s quickly in the canopy, but notice that the petals flop over the top, forming a hood that protects reproductive area to some degree. The lower portion of the flower forms a very rounded drip tip that is not very efficient, but given the heat, wind and tree movement, the surface area dries so quickly, an extensive drip tip is not needed.
Slide 15: This tropical shrub has a reproductive structure called a raceme. It has many, many exposed flowers on branching stems. In most plants the stems point skyward. In this rainforest plant, the droop downward to allow water to drain, forming yets again, a modified driop tip. Water is literally pulled away from the tiny flowers as drips flow downward.
Slide 16: Summary: Tropical flowers that live in rainforests have many ways to manage heavy and prolonged rainfall. From drip tips to large floppy fused petals, they all serve to help the flower dry quickly and avoid disease. Alternatively, some flowers collect rainfall and use it as an attractor for thirsty insects and hummingbirds that pollinate the flowers.
Slide 17: Assessment Opportunity
Slide18: Future Exploration