1.  Leaf epidermal cells as seen in T-section       
      angular or isodiametric (shown in red)....................... 3
1.  Leaf epidermal cells as seen in T-section       
      elliptical................................................... 6

2.  Ventral (abaxial) surface of leaf with 4-10 rows of 
      trapezoidal to diamond shaped, irregularly widened,
      epidermal cells between margin and stomata band; stomata
      4-7-(-9) rows/band; Pacific NW (Taxus brevifolia)............ 3 

                   
                   Taxus brevifolia. Portion of abaxial 
		   surface of leaf from margin to midrib 
                   magnified approx. 250x.

2.  Ventral marginal cells of leaves uniformly rectangular to 
      narrow fusiform; stomata (5-) 7-9 (-11) rows/band............ 5     

3.  Plant a shrub reproducing by layering (branches), forming
      thickets (thicket yew)......... Taxus brevifolia var. reptaneta

       Left: habit of plant growing in shade of valley forest
       along eastern slopes of Cascades in Oregon. Center and
       right: thicket of yew plants in sunny ravine (avalanche 
       shoot) in NW Montana, defoliated and debarked for chemical 
       extraction and isolation of taxol; USFS Forester,
       David Deevy, pointing to layering branch.

3.  Plant a tree reproducing by adventitious shoots from trunks
      or roots..................................................... 4

4.  Columnar trees; leaves radial, seeds ellipsoid; male cones
      maturing in Jul-Aug...................Taxus brevifolia var. nov.

4.  Trees with one to several trunks, not columnar; leaves 
      in nearly a two-ranked arrangement; seeds ovoid, male cones
	maturing May-Jun, usually falling by early Jul............... 4a

4a.  Mature cones with scales persisting only as a cup at base (of 
      cone axis), seed longer than cone axis, usually maturing
      on young branchlets as shown below for both male and 
      female cones (Pacific Yew)....Taxus brevifolia var. brevifolia
                     

	   Var. brevifolia male and female (seed) cones

4a.  Cones with more than one ovule; 
      scales persistent around the cone axis; seed often
      maturing on 2nd yr or older branchlets, notably shorter
      than the cone axis .......... Taxus brevifolia var. polychaeta

	   Var. polychaeta male and female (seed) cones 

5.  Under (abaxial) surface of leaves appearing less papillose 
      on midrib and in marginal zones than in stomata bands; 
      ventral epidermal cells from surface view rectangular to
      slightly wedge shaped; Mexico (Nuevo/Tamaulipas, Veracruz),
      U.S. (Florida, Florida yew)...... Taxus globosa var. floridana

		Var. floridana, abaxial surface from margin to
		midrib in medial region of leaf, magnified about
		250x.

5.  Papillae equally prominent on most of the leaf 
      undersurface to about four cells from margins; 
      ventral (abaxial) epidermal cells on midrib and
      marginal zones mostly fusiform and wavy (incrassate) 
      along cell walls; El Salvador to NE Mexico
      (Mesoamerican Yew)................. Taxus globosa var. globosa

       

     Var. globosa, ventral (abaxial) surface from margin to midrib 
     in medial region of leaf, magnified about 250x, and abaxial 
     midrib cells from fresh leaf magnified 400x.

6.  Stomata bands bordered by smooth marginal and midrib cells, 
      the marginal cells at least 12 across, papillae often
      appearing only within a stomata row; stomata 5-7 (-9) 
      rows/band; NE Atlantic; Taxus canadensis...................  7
6.  Ventral (abaxial) marginal leaf cells usually papillose in
      part, the midrib smooth or papillose; stomata 7-13  
      (-16) rows/band; cultivars................................. 10

7. Trees or shrubs without layering branches, reproducing only 
      by seeds that mature on shoots of the current season; 
      introduced from Japan or Korea (Secrest Arboretum), and 
      with apparent cultivars of hybrid origin...... Taxus biternata
7. Shrubs, usually low, branches often scandent, layering; 
      seeds often on 2nd yr or older branchlets, occasionally 
      on both 1st yr and 2nd yr branchlets........................ 8

8. Main branch with branchlets divided into smaller branchlets
      of equal length (Canada yew.. Taxus canadensis var. canadensis
8. Branchlets simple to unequally divided, mostly alternate to 
      nearly opposite along a main branch (subpinnate)............ 9

9. Leaves widely divergent along two sides of branchlets
    (two-ranked), oblong, obtuse, the blade abruptly narrowed to
    base; rare, Iowa (Rigid-leaf yew)... T. canadensis var. adpressa
9. Leaves bending upwards regardless of branch direction 
      (erect), acute to acuminate, gradually tapering to
      base (Sickle-leaf yew)................T. canadensis var. minor