The Jungle: Orchids and their velamen

Wall of Orchids at Longwood Gardens, displaying some of the diversity

The orchid family is one of the most diverse groups of flowering plants, essentially in a tie for first with the asters. They can roughly be split into two groups based on their growth habit: the terrestrial, or those that live in the ground, and the epiphytic: those that live aerially, often planting themselves in the crotches of branches of canopy trees within the jungle.

Paphiopedilum, a terrestrial orchid

The Jungle was the second biome featured in the Living Planet, and one I found particularly interesting as it depicts a compound ecosystem consisting of three distinct "stacked" habitats where an organism might live: the forest floor, the trunks of trees, or the canopy of these trees. The epiphytic orchids reside in this second layer: not planted in the ground as we tend to think of plants as always being, and not tall enough to have unrestricted access to the sun.

Due to their choice of habitat, the Orchids can't rely on ground water, so must instead draw water from the air of the humid environment around them. In order to accomplish this, they have modified roots, some of which are actually aerial, white or silvery-grey in color, and spongy in texture.  This color and texture results from a covering of velamen, actually the modified epidermis of the root which helps to absorb and hold in water.

An Aerial root on a Phalaenopsis I've acquired

These specialized roots are what often serve as a source of difficulty when many try to grow these in their homes. They assume that due to their native habitat the plant needs a lot of water, and overwater the plant resulting in these roots rotting. They do like this humid environment (some orchids actually wiliting as soon as they're removed from 70-80% humidity), but can't stand having their "feet wet", so to speak.

Probably the most common type of orchid grown, and probably the easiest as well, is the Phalaenopsis, or the Moth Orchid. The common name comes from the floweres, but I feel saying they resemble moths is an understatement. When I first had the opportunity to look at one of these flowers close up, I was taken aback by how accurate this mimicry seems to be, with the center of the flower so approximating the head and eyes of the insect.

Eye to eye, or rather eye column to with a Phalaenopsis

Aggregate of several Phalaenopsis at Longwood Gardens

Last time my Phalaenopsis flowered, I was curious enough to lift up the "moth face" (which is considered the "column" of the flower), curious as to what was underneath. Immediately upon lifting it up, two anther sacs popped out from underneath, exposing the reproductive parts of the flower. This stigma is further below in this structure. The pollinator would inadvertently lift up the "face" or cap of the column when inside the flower, then be covered with the pollen from the anthers, which would be deposited into the stigma when they do the same with another Phalaenopsis flower.

I wish I could show some detailed photos of the column, but couldn't this time around as I took all these at Longwood Gardens. Merkle's Orchids however has a great rundown on orchid flower morphology.

A hybrid containing Cattleya, another popular though more difficult orchid

I'm hoping to get a few more orchids for myself at some point. Planning on trying to grow a Paphiopedilum as well as a Bulbophyllum which I think I'll need to grow in a hanging basket. I was actually going to buy them last year but held off when I learned I'd be moving to Delaware, so I'll see if I can find the money this time around.

A little later this week we're going to revisit Tree ID, and learn how to identify a few Pines.

Fresh Water

Cover art from Wikipedia

I've been rewatching The Living Planet as of late, a classic nature documentary series from David Attenborough (his second actually) which aired in the early to mid 1980s. Though visually it can't quite stack up to some of his more recent work such as Planet Earth, it is interesting to see him taking a more active on-screen role in this series including acts such as narrating the segment on the oceans while in a diving suit, experiencing zero-gravity in a plane during the segment on the skies, and climbing to the top of a canopy tree in the jungle (during which he allegedly left his microphone on, treating his crew to a mix of panic, prayer, and profanity the entire way up).

One thing that really made The Living Planet unique however was that it really focused on the adaptations that various creatures of the earth had developed in order to more successfully survive in their environment. I thought it might be interesting to pick a plant species which would grow in each of these habitats, and cover some of the adaptations or characteristics it displays which allow it to really thrive there.

The first topic covered in the series (at least on the DVD I have, a Christmas Present from my friend Dave a year or two back) is Fresh Water. I actually do have a few photos of freshwater plants which I took upon moving here when I was doing some volunteering at Longwood.

Nymphaea, the Water Lily

Obviously since this plant grows in water instead of upon land, there are a few additional challenges it faces. First off, light does not travel through water as well as air, so it would be difficult for a truly underwater leaf to photosynthesize very effectively. The way the water lily has circumvented this is to ensure that its leaves grow on the surface of the water, able to photosynthesize without losing any of the brightness of the leaf. In fact, in many aquatic plants, the chlorophyll in the leaf tends to be exclusively on the top side, though I'm not sure if this is the case in Nymphaea.

Leaves float (so long as they are alive anyway) due to air pockets within their leaves, which exist due to gas exchange taking place during photosynthesis. It is worth noting how thin and flat this leaf is however, ensuring that water is unlikely to pool up on top of the leaf and cause it to sink.

A Lotus (Nelumbo), at Blithewold

It's not merely the leaves which hold this plant up though. As you can see in the above photo, this plant does have stems connected to these leaves, which in turn connect to roots and anchor it to the bottom of the water body. The shoots tend to be hollow, decreasing their density and encouraging their floating as well.

However, this erroneously sort of portrays the plant as fearing the water. There are obviously a good deal of benefits for the plant resulting from being submerged in water. For one, water retention becomes a non-issue. Land plants have stomates (stomata) in their leaves, essentially pores for gas exchange. They try to keep these closed as much as possible to reduce transpiration. Since aquatic plants don't have to worry about drying out, their stomata tend to be open most of the time.

So, suffice to say, plants can grow just fine in the water, as long as they can keep their leaves out of it.

I actually forget what this is, but note that even though the margins of the leaves are raised, there are still "gabs" through which the water could run off were the leaf to become submerged. I think this plant may have actually had a few other tissues which aided in its floating but can't quite remember... I'll have to check back in the summer.

I'm not sure how regularly I'm going to do these (I'd like to do some more Tree ID over the next few weeks), but the next one will probably be on the Jungle, focusing on how epiphytic orchids use their roots (and probably a bit more on orchids as well as I want to get down to the Longwood Orchid show and take some pictures).