A Fragrant, Monoecious Flower

So it is not quite possible to have a "monoecious flower" because the definition of monoecious applies to entire plants. Monoecious (which means "one household" or one ecos) plants produce flowers that are unisexual - male and female - and both kinds of flowers are found on the same individual plant. This contrasts with dioecious plants, which also bear unisexual flowers. But a dioecious plant keeps two households, and an individual plant produces only male or female flowers. The reason we bother to distinguish these habits in the first place is that most plants produce flowers that are perfect: a single flower has both male (the pollen-producing stamens) and female (egg-producing pistils) parts.

The timeliness in talking about a monoecious flower relates to flowering of the Titan Arum, Amorphophallus titanum. One of the many Titan Arum plants at The Huntington is coming into flower; people call it the Stinky Plant. People also call it the largest flower in the world because it certainly looks like a single flower. But to a botanist the Titan Arum is really a massive and glorious cluster of flowers, an inflorescence, that looks like a single flower. Every plant in the arum family does this, and all follow a similar pattern; tiny flowers are clustered along a narrow stem called the spadix. The flowers may be perfect, having both stamens and pistils. But in many, pistillate flowers are produced along one zone of the axis while staminate flowers grow in a separate zone. Surrounding the spadix is an impressive, petal-like leafy bract called a spathe.

In some members of the arum family, like Philodendron, the spathe completely surrounds the spadix - opening only at the very tip. In others, like Spathiphyllum and Anthurium, the spathe doesn't surround the spadix at all. A whole bunch of aroids have a spathe that surrounds the base of the spadix, and then opens up entirely, making a hood. This is what plants in the genus Arum do.

The spathe may lack a hood, simply cupping around the spadix. This is the story for the most spectacular of the arums, the lowland tropical Titan Arum. And everything about this plant seems extraordinary, from seed to flower. When a seed germinates, it makes a simple underground stem called a corm, and a single leaf. Seasonally, the leaf withers and falls off; with a new growth season the enlarged corm produces another single leaf, but much larger. Several cycles of growth yield an increasing larger corm and leaf, to the point that the single leaf grows to a height of over 8 feet, with a spread of over 6 feet. The petiole of the leaf is so large that you can't wrap your hands completely around it.

At some point the plant has reached a sufficient size to flower. When that happens, the cycle is interrupted. Instead of another single leaf, the flowering stem is produced, a massive and beautiful elaboration. As soon as the flowering stalk breaks the surface of the soil, it is clearly not the normal leaf. Within just a few weeks, the inflorescence (the spadix) grows to 4-5 feet tall, tightly enrobed by the spathe. At maturity, the spathe unfolds, forming a flared vase that is deep maroon purple on its upper surface. Projecting from and presiding over the vase is the inflated spadix - but the visible portion is sterile. The male and female flowers are clustered in zones down inside the vase-like portion of the spathe, but they do not mature on the same day.

The female flowers mature first, and are receptive before the pollen is ready. Very soon after that, the male flowers mature and release the pollen. In nature, the inflorescence attracts flies, which arrive and crawl over the flowers. If the flies already have visited a Titan Arum, they may well come already covered with pollen, and therefore pollinate the female flowers. If not, then perhaps they will leave the Titan Arum with pollen which is carried to the next flower they visit. But what do the flies get out of this?

Well not much. It's a false alarm for them. Flies come to the Titan Arum expecting to find rotting meat. The spathe even has a dark flesh color, but the color is not what draws flies. It is the fragrance that draws flies; the alluring, decomposing protein aroma of rotting flesh. People can smell it also, but we are generally repelled by odors that many flies find irresistible. So the flies come, and they hang around. When the party is over, the flies leave. Though completely duped by the flower, the flies do not hesitate to visit a second or third if it is available.

After just a few days, the entire structure collapses in a sodden mass. If pollination and fertilization were successful, then seed begin to form in bright orange-red fruit, and a new generation is ready. But the parent plant is not especially caput. As long as the corm is intact, the vegetative cycle begins anew. Once the corm mass is restored, then the plant might bloom again. A plant that bloomed at The Huntington in 1999 flowered again in 2002, and persists to this day, slowly gaining leaf size from one growth cycle to the next.