Taxonomy of Flowering Plants - LECTURE NOTES - Spring, 1998
Hugh D. Wilson - rm. 306, Butler Hall
9 March 1998
The Dilleniidae

Family Overviews - The Nepenthales

The three families placed by Cronquist in his Nepenthales are linked, to a certain extent, by floral features that allow this alignment.  However, the group is not well defined from a structural point of view and the three families are treated in various ways in other classification systems.  We touch on this group only to point out an interesting reversal of biotic roles (animals consumed by plants) brought about by adaptations for growth in low nitrogen environments.  Most angiosperms secure this fundamental element from the soil and, if it is not available, the niche is not occupied.   Taxa of the Nepenthales have evolved ways around the nitrogen problem, i.e., extracting it from animals - mostly arthropods - via clever structural and biochemcial innovations.  From a floristic point of view, few of the species mentioned below are common elements of our flora.  They are, however, usually present in low frequencies and, if you run across one, you are usually in an interesting habitat.

Nepenthaceae - the Tropical Pitcher Plant Family
  
 
 

A monotypic family (only the Genus Nepenthes) of about 75 species - mostly epiphytic, perennial herbs - distributed across the Old World tropics:  Seychelles, Indomalayan region, Madagascar, Ceylon, tropical Australia, New Caledonia.  Leaves, or more often leaf tips, modified to form 'pitchers' that both catch and 'digest' prey. (images derived from DELTA and University of Hawaii Botany)

Sarraceniaceae - the Pitcher Plant Family
 
Three genera and about 15 herbaceous, perennial species distributed in bogs of eastern North America (Sarracenia), western North America (Darlingtonia), and northeastern South America (Heliamphora).  Leaves also modified to form 'pitchers' that both catch and 'digest' prey.
 

  Sarracenia alata - the only Texas species
 

  Sarracenia alata - past anthesis, androecium gone - peltate stigma

  Sarracenia alata - dehising capsule
 
 

Droseraceae - the Sundew Family


Dionaea muscipula


Drosera annua

 A family of four genera, 3 monotypic, all herbs.  The sundew Genus - Drosera -  includes about 100 species distributed world wide, that have evolved a 'flypaper' leaf with movable, mucilage-tipped tentacle trichomes.  We have three Drosera species in Texas and one, D. annua, is common (but not conspicuous) in open sandy sites of our Post Oak woodlands. 

The single species of Dionaea, D. muscipula, endemic to the southeastern U.S., features leaves that have evolved to form an active trap mechanism

Drosera - leaf
 

  Dionaea muscipula - lunching on cranefly

  Dionaea muscipula - a close look at 'trigger' trichomes on leaf trap
 

More information on the Sarraceniaceae , Droseraceae, or Nepenthaceae

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