Xeric World Forums  

Go Back   Xeric World Forums > Featured Discussion Forums > Other Xeric Plants

Other Xeric Plants General category for discussion of species that do not fall into the defined categories

Reply
 
Thread Tools Display Modes
  #1  
Old 02-23-2011, 01:31 PM
agavegreg's Avatar
agavegreg agavegreg is offline
Ready to Mulch
 
Join Date: Feb 2009
Location: Tucson
Posts: 1,261
agavegreg is on a distinguished road
Default Adaptations of Xeric Plants

I am developing a 2 hour class, for the layperson, on plant adaptations to drought and would like to ask the XericWorld community for feedback.

I have two broad categories for the adaptations: Drought Avoidance and Drought Tolerance. I found a paper that has these categories plus one they called Drought Escape (which I feel should be included in Drought Avoidance) and the adaptations. Under Drought Avoidance the adaptations are enhanced water uptake and reduced water loss. However, I have always viewed those more as Drought Tolerance mechanisms. The adaptations for Drought Tolerance are osmotic adjustments, antioxidant capacity and dessication tolerance.

I'm looking at adaptations such as annuals and perennials, small leaves, waxy coatings, deciduous leaves, extensive root systems, crinkly leaves deflecting airflow, succulence. Any other suggestions? Also, based on the mechanisms listed above, which of the two categories, DA or DT, would each adaptation fall into? Any thoughts and feedback would be appreciated.

Thanks.
Greg
Reply With Quote
  #2  
Old 02-23-2011, 04:07 PM
Boo Hollow's Avatar
Boo Hollow Boo Hollow is offline
Ready to Mulch
 
Join Date: Aug 2010
Location: Aromas
Posts: 1,567
Boo Hollow is on a distinguished road
Default CAM I am

Greg- I think that the CAM process would also be fundamental to drought tolerance. Other items would be waxy coatings, reflective coatings and to echo Baja Costero - spines and hairs not only increase uptake of air moisture, they are radiators for heat loss as well.

On a more detailed note, Mycorhizial relations may also play a role.

Von Willert's work on Survival Strategies of Desert Plants would also be a good reference. I am sure the group will have lots of input.
Reply With Quote
  #3  
Old 02-23-2011, 05:22 PM
Matt Maggio's Avatar
Matt Maggio Matt Maggio is offline
Ready to Mulch
 
Join Date: Apr 2009
Location: Van Nuys, CA
Posts: 1,003
Matt Maggio is on a distinguished road
Default

I'm sorta with with Baja Costero... Isn't it mostly drought tolerance? I mean, if the plant is existing during the event? Even species that we find in shaded crevices, shaded slope aspects, under nurse plants or in riparian corridors are not avoiding the drought. Their seeds may have landed in these more sheltered places and more harsh places, all may have germinated under brief conditions of favorability, but only the former survived to pass on their genes. How are species that live in a riparian corridor, for instance, avoiding drought any more than perennial species from wetter climates?

I think if one could make a case for drought avoidance, it could be with annuals. They are programmed to expire in spite of varying levels of moisture between microclimates. That's in addition to an individual plant only being able to survive while conditions are favorable. Here in California, we had significant rainfall in late 2010 , then six weeks of mild weather and no rain. The annuals already started dying off before the rains returned just recently. Many won't be coming back to life regardless. Their seeds will set and lay dormant until conditions and daylength are once again favorable.

So, this is for the layperson... hmmm? Many of the fundamentals have already been brought up.

You could talk about seed dormancy and how seeds of many drought resistant species can stay dormant for a long period of time. Some require heavy rain to wash away germination inhibitors. Many drought adapted or avoiding species also produce large numbers to ensure recruitment.

CAM is a great one, and you may also add the C4 pathway for warm season monocots. I would talk about the stomata and how they are recessed inside 'stomal crypts' on some succulents species. Such would discourage evapotranspiration.

You could talk about some succulent types having extensive shallow root systems to take advantage of brief, fickle downpours... or talk about how some desert trees and shrubs have deep root systems to reach the water table.

The relatively low surface area/volume ratios of succulents for water conservation purposes.

The expanding/contracting action of the ribs on cacti, which allow for gorging on unreliable rainfall.

I'll think some more...

Matt
Reply With Quote
  #4  
Old 02-23-2011, 10:03 PM
agavegreg's Avatar
agavegreg agavegreg is offline
Ready to Mulch
 
Join Date: Feb 2009
Location: Tucson
Posts: 1,261
agavegreg is on a distinguished road
Default

Thanks for the input so far. The drought avoidance is a very narrow category and pretty much confined to annuals and perennials. Now when I say perennials, I mean plants that grow, flower and set seed during the rainy season and then die back to a rootstock, bulb or corm. As opposed to a plant that grows, flowers and sets seed every year for more than 2 years.


Here is what I have so far for Drought Tolerance
a. waxy coatings on leaves
b. small leaves
c. deciduous leaves
d. crinkly leaves
e. shallow, extensive root systems
f. succulence
g. CAM
h. rosette form directing water to plant base
i. spines as water collectors and for heat dissipation
j. C4 plants
Reply With Quote
  #5  
Old 02-24-2011, 12:30 AM
Allen Repashy's Avatar
Allen Repashy Allen Repashy is offline
Administrator
 
Join Date: Oct 2008
Location: Bonsall
Posts: 1,113
Allen Repashy has disabled reputation
Default

Quote:
Originally Posted by agavegreg View Post
Thanks for the input so far. The drought avoidance is a very narrow category and pretty much confined to annuals and perennials. Now when I say perennials, I mean plants that grow, flower and set seed during the rainy season and then die back to a rootstock, bulb or corm. As opposed to a plant that grows, flowers and sets seed every year for more than 2 years.


Here is what I have so far for Drought Tolerance
a. waxy coatings on leaves
b. small leaves
c. deciduous leaves
d. crinkly leaves
e. shallow, extensive root systems
f. succulence
g. CAM
h. rosette form directing water to plant base
i. spines as water collectors and for heat dissipation
j. C4 plants
How about leaf color..... blue/silver seems to correspond to heat/cold tolerance... I think. LOL

Also, as far as roots go..... some plants put down deep tap roots to reach the water table.... others have really fat roots (not necessarily succulent plants) to store moisture..
Reply With Quote
  #6  
Old 02-24-2011, 02:45 AM
Chanin's Avatar
Chanin Chanin is offline
Well Established
 
Join Date: Jan 2011
Location: Bangkok
Posts: 124
Chanin is on a distinguished road
Default

There are many window-leaf ( fenestrate leaf) adaptation succulents such as Lithop, Harworthia.
Should it be included?
Reply With Quote
  #7  
Old 02-24-2011, 03:05 AM
Chanin's Avatar
Chanin Chanin is offline
Well Established
 
Join Date: Jan 2011
Location: Bangkok
Posts: 124
Chanin is on a distinguished road
Default

Just notice some of my caudiciforms which form a kind of Cork bark in Beaucarnea spp., Pseudobombax, Dioscorea
Corrugate texture of caudex in Adenia spp, Opercuricarya and also Peel bark in Cyphostemma spp.
Reply With Quote
  #8  
Old 02-24-2011, 03:55 AM
Chanin's Avatar
Chanin Chanin is offline
Well Established
 
Join Date: Jan 2011
Location: Bangkok
Posts: 124
Chanin is on a distinguished road
Default

Hi again, just walked around my xeric garden to find some more characteristics,
how about the hygroscopic (resurrection) plant!? In this case I found some xeric type bromeliads:
most of Tillandsia which was withered from the drought will become firm and ample by absorbing water within a few hours.
Reply With Quote
  #9  
Old 02-24-2011, 02:40 PM
Tim Harvey's Avatar
Tim Harvey Tim Harvey is offline
Ready to Mulch
 
Join Date: Jan 2009
Location: Thousand Oaks
Posts: 1,325
Tim Harvey is on a distinguished road
Default

There are various plants that concentrate locally scarce water through leaf architecture, such as Welwitschia mirabilis and Rheum palaestinum. Eulychnia spp. trap moisture from fog.

T
Reply With Quote
  #10  
Old 02-24-2011, 04:04 PM
Andy Andy is offline
Ready to Cone
 
Join Date: Feb 2010
Location: San Diego
Posts: 281
Andy is on a distinguished road
Default

Many bromeliads have water impounding leaves, not to mention the trichomes that in some genera help draw in moisture as well as give some protection from strong sun. Look to epiphytes as they will have adaptations to their local drought as they do not have root access to soil moisture. Some orchids photosynthesize in their roots so they don't need as much leaf surface area which should help conserve water.
Reply With Quote
  #11  
Old 02-24-2011, 04:43 PM
Boo Hollow's Avatar
Boo Hollow Boo Hollow is offline
Ready to Mulch
 
Join Date: Aug 2010
Location: Aromas
Posts: 1,567
Boo Hollow is on a distinguished road
Default Ocotillo

Quote:
Originally Posted by Andy View Post
Many bromeliads have water impounding leaves, not to mention the trichomes that in some genera help draw in moisture as well as give some protection from strong sun. Look to epiphytes as they will have adaptations to their local drought as they do not have root access to soil moisture. Some orchids photosynthesize in their roots so they don't need as much leaf surface area which should help conserve water.
Andy - You bring up a good point. Fouquieria splendens and others can conduct phtosynthesis through their bark. This would be another adapatation to allow survival and engery fixation without the need for leaves.

The more people write, the more amazing the plants that we all enjoy must come to be.
Reply With Quote
  #12  
Old 02-24-2011, 06:38 PM
madabouteu's Avatar
madabouteu madabouteu is offline
Ready to Clone
 
Join Date: Aug 2009
Location: Gadsden
Posts: 392
madabouteu is on a distinguished road
Default

I am not sure how to fit this in, but it's something I bring up when I talk about caring for succulents - it's not a concept I invented but was mentioned in a book I read.

You can divide succulents into two groups, when it comes to caring for them. First are the drought-tolerant plants like agaves and aloes, which in growing season welcome as much water as you are willing to give. The second group consists of plants like Lithops, which pretty much cannot tolerate a surplus of water. In other words, they are so well adapted to a scarcity of water that they cannot handle a surplus of it. This may not be applicable to your talk, though. And in any case (in the words of an old saying) no generalization is worth a darn, including this one.
Reply With Quote
  #13  
Old 02-24-2011, 09:06 PM
Tim Harvey's Avatar
Tim Harvey Tim Harvey is offline
Ready to Mulch
 
Join Date: Jan 2009
Location: Thousand Oaks
Posts: 1,325
Tim Harvey is on a distinguished road
Default

Flowering at night - though this has evolved possibly independently for several unrelated reasons.

T
Reply With Quote
  #14  
Old 02-26-2011, 11:35 PM
Addictedtoagaves's Avatar
Addictedtoagaves Addictedtoagaves is offline
Ready to Mulch
 
Join Date: Nov 2010
Location: West of Phoenix
Posts: 1,330
Addictedtoagaves is on a distinguished road
Default

Quote:
Originally Posted by Boo Hollow View Post
Andy - You bring up a good point. Fouquieria splendens and others can conduct phtosynthesis through their bark. This would be another adapatation to allow survival and engery fixation without the need for leaves.

The more people write, the more amazing the plants that we all enjoy must come to be.
The Circidium species of trees do this with their green bark.
Reply With Quote
  #15  
Old 02-26-2011, 11:47 PM
agavegreg's Avatar
agavegreg agavegreg is offline
Ready to Mulch
 
Join Date: Feb 2009
Location: Tucson
Posts: 1,261
agavegreg is on a distinguished road
Default

Thanks for the additions, those are great.

Tim, why would night flowering be an adaptation to a xeric environment? Reduced water loss through the flowers?

Greg
Reply With Quote
  #16  
Old 02-27-2011, 12:12 PM
wantonamara's Avatar
wantonamara wantonamara is offline
Ready to Mulch
 
Join Date: Jul 2010
Location: Dripping Springs
Posts: 798
wantonamara is on a distinguished road
Default

Maybe because the polinators they need are out at night and not out in the blazing sun and heat. It is easier to be a flower at night and get the job of providing pollin before withering. That's my un unscientific guess.
Reply With Quote
  #17  
Old 03-01-2011, 03:32 AM
cactuschris cactuschris is offline
Rhizome
 
Join Date: Feb 2011
Location: Hartford
Posts: 16
cactuschris is on a distinguished road
Default

How about parasites, thay use other's strategies.
Also shade lovers that shelter under 'mother plants', or even those that live on cliffs facing away from the sun.
There are also a group that face the sun so as to reduce the surface area exposed (I think Pachypodium namaquensis does this ??)

chris
Reply With Quote
  #18  
Old 03-02-2011, 11:21 PM
rnixon's Avatar
rnixon rnixon is offline
Bulbil
 
Join Date: Mar 2009
Location: Tucson
Posts: 26
rnixon is on a distinguished road
Default

Greg,

Don't forget to discuss one of the most unique and ecophysiologically advanced (my opinion) succulent plant genera:

The poikilohydric and practically astomate cacti of the mighty genus...BLOSSFELDIA!!!!!!!





Reply With Quote
  #19  
Old 03-03-2011, 12:25 PM
agavegreg's Avatar
agavegreg agavegreg is offline
Ready to Mulch
 
Join Date: Feb 2009
Location: Tucson
Posts: 1,261
agavegreg is on a distinguished road
Default

Right on. Thanks Rob! I'll certainly be sure to talk about that hybrid of Resurrection Fern and Mammillaria.

Quote:
Originally Posted by rnixon View Post
Greg,

Don't forget to discuss one of the most unique and ecophysiologically advanced (my opinion) succulent plant genera:

The poikilohydric and practically astomate cacti of the mighty genus...BLOSSFELDIA!!!!!!!




Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -4. The time now is 06:54 PM.


Powered by Very Little Water Version 3.7.4
All content and images are copyright Xeric World Forums