The unifacial cambium (pl. cambia or cambiums) produces cells to the interior of its cylinder. These cells differentiate into
xylem
Xylem is one of the two types of transport tissue in vascular plants, the other being phloem. The basic function of xylem is to transport water from roots to stems and leaves, but it also transports nutrients. The word ''xylem'' is derived from ...
tissue. Unlike the more common bifacial
cambium
A cambium (plural cambia or cambiums), in plants, is a tissue layer that provides partially undifferentiated cells for plant growth. It is found in the area between xylem and phloem. A cambium can also be defined as a cellular plant tissue from w ...
found in later
woody plants
A woody plant is a plant that produces wood as its structural tissue and thus has a hard stem. In cold climates, woody plants further survive winter or dry season above ground, as opposite to herbaceous plants that die back to the ground until sp ...
, the unifacial cambium does not produce
phloem
Phloem (, ) is the living biological tissue, tissue in vascular plants that transports the soluble organic compounds made during photosynthesis and known as ''photosynthates'', in particular the sugar sucrose, to the rest of the plant. This tran ...
to its exterior. Also in contrast to the bifacial cambium, the unifacial cambium is unable to expand its circumference with anticlinal cell division. Cell elongation provides a limited amount of expansion.
Unifacial cambium plant morphology and life cycles
The unifacial cambium allowed plants to grow as tall as 50 metres. Lacking secondary phloem, unifacial cambium plants developed alternative strategies to long range nutrient transport. For example, the stems of
lycophyte
The lycophytes, when broadly circumscribed, are a vascular plant (tracheophyte) subgroup of the kingdom Plantae. They are sometimes placed in a division Lycopodiophyta or Lycophyta or in a subdivision Lycopodiophytina. They are one of the oldest ...
trees were covered in photosynthesizing leaf bases.
Due to the limited capacity for circumference growth, unifacial cambium plants had very little wood compared to modern woody plants. Xylem tissue in unifacial cambium plants was particularly structurally efficient. Additional structural support was provided in lycophytes by a special periderm tissue in the outer cortex.
Lycophyte trees exhibit determinate growth. These trees appear to have lived for most of their life cycle as a 'stump', establishing root networks underground, before shooting up rapidly, releasing spores, and dying shortly thereafter.
External links
'Key innovations, convergence, and success: macroevolutionary lessons from plant phylogeny', article by Michael J. Donahue from ''Paleobiology'' 31(2), 2005 (pdf)
Plant physiology
Plant anatomy