Pitcher development and evolution
Apr 16, 2008 7:56:37 GMT -10
Post by unclemasa on Apr 16, 2008 7:56:37 GMT -10
Evolution of the Nepenthes Pitcher: A Fantasy in Pictures and Drawings
Disclaimer:
This is my imagined evolution of the Nepenthes pitcher. Along the way I make numerous undocumented, unwarranted, wildly speculative and probably erroneous assumptions. I’ve decided not to let this stop me! My purpose is not to establish fact but rather to stimulate discussion.
We begin with the assumption that, the ”Winged” form of N. mirabilis is primitive in it's leaf, tendril and pitcher development and that those species of Nepenthes with very well defined pitchers and tendrils evolved later in time than the “winged” N. mirabilis.
Here are a few pictures of N. mirabilis, winged .....
We will next assume that primitive Nepenthes had basically the same leaf structure and dimensions as those of today but minus the bare tendril and pitcher. This seem a fair enough assumption as, other than the pitcher and tendril, the leaf morphology is similar to many other tropical plants.
Under this assumption then, the primitive leaves of early Nepenthes were long and flowing structures similar to the ones in this picture ......
A critical part of the conjecture will be that Nepenthes leaves lend themselves to the accidental containment of water. To make this point you should understand a few facts about the way the leaves of Nepenthes unfurl.
Here are a few shots of some typical Nepenthes leaves as they unfurl .....
note how the leaves unfurl bilaterally from the top center outward .....
Even after the leaf is fully unfurled the sides of the leaf blade often remain reflexed bilaterally upward on either side of the midrib.
There are, of course, differing leaf morphologies among the various species of Nepenthes but, for the purpose of our conjecture, we will assume that primitive Nepenthes had mirabillis-type leaves that retain this slightly reflexed geometry.
Pitcher Formation ......
The very long leafed, low growing, primitive ancestor of Nepenthes grew in swampy conditions with it’s long, reflexed leaves laying along the ground in the fashion of this rosette N. anamensis .......
note: The above picture and other plants photographs show plants growing in pots and thus the tips of the leaves are elevated and not sprawled across the terrain as they would be if they were growing in the ground. With this kind of sprawling growth pattern it would not be uncommon for a forming, or newly formed, leaf to encounter an obstacle inhibiting it from it’s normal expansion and growth pattern.
FIGURE 1
FIGURE 2
Forming a pocket ......
Due to the leaf’s structural characteristics an upward deflection of the growing tip pushes back along the axis of the center rib and creating folds in of the leaf blades on either side of the rim and the formation of a valley, or pocket, a short distance back of the leaf apex. If the forces are great enough then, the elevation of the leaf tip can cause a fracture in the leafs midrib and the most extreme part of the lower curve.
Another cause of pocket formation would be obstructions to the complete unfurling of a new leaf ......
FIGURE 3
The retention of water .....
The formation of pockets of water on the leaves of plants is common place. It is not difficult to imagine a large leaf, having encountered some obstruction in unfurling or development, forming a valley or small pocket where, due to ample rain and high humidity, it retains a small amount of water.
In the next picture we have the leaf of a Nepenthes campanulata showing that even the firmer and flatter leaves of some species often trap pockets of water.
note: also in this picture you will notice that this water quickly becomes a small ecosystem of debris and bacteria.
FIGURE 4
In a relatively short time, this tiny pool of standing water can become a home to bacteria and other micro-organisms.
FIGURE 5
The molecular magic ......
Water is the perfect medium for the exchange of genetic material between bacteria and plant. Our supposed crack, or wound, in the leaf tissue provides a path around the tougher outer layers of cells that form the leaf’s surface and into the interior of the plant.
Alien bits of bacterial genetic material find their why into the plants DNA and cause a heritable mutation in the cells around wound and in future generations cause the production of a new type of cell structure in the plant ... one that produces digestive enzymes.
FIGURE 6
In future generations, born of the wounded plant the message was repeated and modified. When conditions were right certain genes located in the same area of the leaf where it’s ancestor was wounded turn on and commence the production of these new cellular structures. Our plant has now become carnivorous.
Here is a “freak” leaf showing the development of glandular material in the center of the leaf.
radiant expansion .......
The rapid growth of these new glandular structures consume space previously reserved for leaf blade material and initiate a 360 degree dynamic of expansion around the glandular growth, i.e., The leaf blade materials that previously occupied the space now consumed by glandular structures are displaced from the center of the blade and forced toward the perimeters of the leaf.
FIGURE 7
The continued growth of the glandular area in the center of the leaf, combined with the existing structural dynamic of the leaf leads to the formation of a proto-pitcher .....
FIGURE 8
The ease with which the leaf adapts to this formation is demonstrated in the following picture. (I was easily able to achieve this formation with only one hand.)
At this point the plant has developed to the near 3/4 stage in the production of a pitcher and begins to resemble the pitchers of winged mirabilis .....
FIGURE 9
Next in the process of pitcher construction is a series of cellular fusions that join the edges of the leaf in order to complete the enclosure. With the filling in of the gap between the leaf edges our leaf has now taken the form of a tube. At the same time, the fimbriate edges of the leaf become extremely exaggerated and produce what will become the wings of the pitcher and the ribs of the future peristome.
FIGURE 10
Here is a very interesting picture of a plant grown by Geoff and Andrea Mansell of Exotica Plants.
And another "freak" from my own collection ...
We are now very close to having developed, from our original leaf, a fully formed pitcher. All that remains is to explain the development of the pitcher lid and the peristome.
In our story, new growth fills in the gap at the top of our tube and begins forming what will become the pitcher lid.
FIGURE 11
Beneath the new material of the pitcher lid, the fimbriate edges of the leaves have expanded and elongated to form what will become the peristome.
FIGURE 12
In order to explain the opening of the lid we postulate a differential expansion or growth rate for the materials forming the peristome and those forming the lid, i.e., the peristome continues to develop from the fimbriate edges of the leaf and in the later stages of development out-pace the growth of the material that forms the pitcher lid.
The different expansion rates of the lid and peristome materials result in the fracture of the materials that join the two together at all points except the apex of the peristome. The faster growth rate at the tip of the leaf then out-paces that of the lower portion of the pitcher and draws the lid open.
FIGURE 15
We now have a fully formed pitcher.
Tendril development ....
The cellular fusions and the building of the peristome and lid make huge energy demands on the leaf tissues and these demands are meet by cutting energy costs in other areas. To this end, the leaf sacrifices some of its surface area by curtailing the development of the leaf blade in all but the portion of the leaf nearest the stem and retains only the midrib or ‘tendril’.
Disclaimer:
This is my imagined evolution of the Nepenthes pitcher. Along the way I make numerous undocumented, unwarranted, wildly speculative and probably erroneous assumptions. I’ve decided not to let this stop me! My purpose is not to establish fact but rather to stimulate discussion.
We begin with the assumption that, the ”Winged” form of N. mirabilis is primitive in it's leaf, tendril and pitcher development and that those species of Nepenthes with very well defined pitchers and tendrils evolved later in time than the “winged” N. mirabilis.
Here are a few pictures of N. mirabilis, winged .....
We will next assume that primitive Nepenthes had basically the same leaf structure and dimensions as those of today but minus the bare tendril and pitcher. This seem a fair enough assumption as, other than the pitcher and tendril, the leaf morphology is similar to many other tropical plants.
Under this assumption then, the primitive leaves of early Nepenthes were long and flowing structures similar to the ones in this picture ......
A critical part of the conjecture will be that Nepenthes leaves lend themselves to the accidental containment of water. To make this point you should understand a few facts about the way the leaves of Nepenthes unfurl.
Here are a few shots of some typical Nepenthes leaves as they unfurl .....
note how the leaves unfurl bilaterally from the top center outward .....
Even after the leaf is fully unfurled the sides of the leaf blade often remain reflexed bilaterally upward on either side of the midrib.
There are, of course, differing leaf morphologies among the various species of Nepenthes but, for the purpose of our conjecture, we will assume that primitive Nepenthes had mirabillis-type leaves that retain this slightly reflexed geometry.
Pitcher Formation ......
The very long leafed, low growing, primitive ancestor of Nepenthes grew in swampy conditions with it’s long, reflexed leaves laying along the ground in the fashion of this rosette N. anamensis .......
note: The above picture and other plants photographs show plants growing in pots and thus the tips of the leaves are elevated and not sprawled across the terrain as they would be if they were growing in the ground. With this kind of sprawling growth pattern it would not be uncommon for a forming, or newly formed, leaf to encounter an obstacle inhibiting it from it’s normal expansion and growth pattern.
FIGURE 1
FIGURE 2
Forming a pocket ......
Due to the leaf’s structural characteristics an upward deflection of the growing tip pushes back along the axis of the center rib and creating folds in of the leaf blades on either side of the rim and the formation of a valley, or pocket, a short distance back of the leaf apex. If the forces are great enough then, the elevation of the leaf tip can cause a fracture in the leafs midrib and the most extreme part of the lower curve.
Another cause of pocket formation would be obstructions to the complete unfurling of a new leaf ......
FIGURE 3
The retention of water .....
The formation of pockets of water on the leaves of plants is common place. It is not difficult to imagine a large leaf, having encountered some obstruction in unfurling or development, forming a valley or small pocket where, due to ample rain and high humidity, it retains a small amount of water.
In the next picture we have the leaf of a Nepenthes campanulata showing that even the firmer and flatter leaves of some species often trap pockets of water.
note: also in this picture you will notice that this water quickly becomes a small ecosystem of debris and bacteria.
FIGURE 4
In a relatively short time, this tiny pool of standing water can become a home to bacteria and other micro-organisms.
FIGURE 5
The molecular magic ......
Water is the perfect medium for the exchange of genetic material between bacteria and plant. Our supposed crack, or wound, in the leaf tissue provides a path around the tougher outer layers of cells that form the leaf’s surface and into the interior of the plant.
Alien bits of bacterial genetic material find their why into the plants DNA and cause a heritable mutation in the cells around wound and in future generations cause the production of a new type of cell structure in the plant ... one that produces digestive enzymes.
FIGURE 6
In future generations, born of the wounded plant the message was repeated and modified. When conditions were right certain genes located in the same area of the leaf where it’s ancestor was wounded turn on and commence the production of these new cellular structures. Our plant has now become carnivorous.
Here is a “freak” leaf showing the development of glandular material in the center of the leaf.
radiant expansion .......
The rapid growth of these new glandular structures consume space previously reserved for leaf blade material and initiate a 360 degree dynamic of expansion around the glandular growth, i.e., The leaf blade materials that previously occupied the space now consumed by glandular structures are displaced from the center of the blade and forced toward the perimeters of the leaf.
FIGURE 7
The continued growth of the glandular area in the center of the leaf, combined with the existing structural dynamic of the leaf leads to the formation of a proto-pitcher .....
FIGURE 8
The ease with which the leaf adapts to this formation is demonstrated in the following picture. (I was easily able to achieve this formation with only one hand.)
At this point the plant has developed to the near 3/4 stage in the production of a pitcher and begins to resemble the pitchers of winged mirabilis .....
FIGURE 9
Next in the process of pitcher construction is a series of cellular fusions that join the edges of the leaf in order to complete the enclosure. With the filling in of the gap between the leaf edges our leaf has now taken the form of a tube. At the same time, the fimbriate edges of the leaf become extremely exaggerated and produce what will become the wings of the pitcher and the ribs of the future peristome.
FIGURE 10
Here is a very interesting picture of a plant grown by Geoff and Andrea Mansell of Exotica Plants.
And another "freak" from my own collection ...
We are now very close to having developed, from our original leaf, a fully formed pitcher. All that remains is to explain the development of the pitcher lid and the peristome.
In our story, new growth fills in the gap at the top of our tube and begins forming what will become the pitcher lid.
FIGURE 11
Beneath the new material of the pitcher lid, the fimbriate edges of the leaves have expanded and elongated to form what will become the peristome.
FIGURE 12
In order to explain the opening of the lid we postulate a differential expansion or growth rate for the materials forming the peristome and those forming the lid, i.e., the peristome continues to develop from the fimbriate edges of the leaf and in the later stages of development out-pace the growth of the material that forms the pitcher lid.
The different expansion rates of the lid and peristome materials result in the fracture of the materials that join the two together at all points except the apex of the peristome. The faster growth rate at the tip of the leaf then out-paces that of the lower portion of the pitcher and draws the lid open.
FIGURE 15
We now have a fully formed pitcher.
Tendril development ....
The cellular fusions and the building of the peristome and lid make huge energy demands on the leaf tissues and these demands are meet by cutting energy costs in other areas. To this end, the leaf sacrifices some of its surface area by curtailing the development of the leaf blade in all but the portion of the leaf nearest the stem and retains only the midrib or ‘tendril’.
