Discussion in relation to previous studies

Metcalfe and Chalk (1957) briefly characterized Urtica dioica.

The family is divided into two major groups:

The Forsskaolea/Parietaria/Gesnouinia group represents typical stems with a continuous vessel-fiber-ray xylem. The Urtica group has permanent vascular bundles and tangential bands of thin-walled parenchyma. This type of xylem is unique for Angiospermae.

Present features in relation to the number of analyzed species

IAWA code frequency

Present features in relation to the number of analyzed species

IAWA code frequency

Total number of species

10

1

growth rings distinct and recognizable

5

2

growth rings absent

4

2.1

only one ring

1

4

semi-ring-porous

1

5

diffuse-porous

5

6

vessels in intra-annual tangential rows

3

9

vessels predominantly solitary

3

9.1

vessels in radial multiples of 2-4 common

8

10

vessels in radial multiples of 4 or more common

2

11

vessels predominantly in clusters

1

13

vessels with simple perforation plates

10

20

intervessel pits scalariform

10

22

intervessel pits alternate

10

41

earlywood vessels: tangential diameter 50-100 pm

10

50

<100 vessels per mm2 in earlywood

7

50.1

100-200 vessels per mm2 in earlywood

2

56

tylosis with thin walls

10

61

fiber pits small and simple to minutely bordered

(<3 pm = libriform fibers)

10

68

fibers thin-walled

2

70

fibers thin- to thick-walled

9

70.2

tension wood present

6

76

parenchyma apotracheal, diffuse and in aggregates

1

79

parenchyma paratracheal

10

85

axial parenchyma bands more than three cells wide,

Ficus/Urtica type

4

89

parenchyma marginal

2

97

ray width predominantly 1-3 cells

3

98

rays commonly 4-10-seriate

5

99

rays commonly >10-seriate

5

99.1

vascular bundle form remaining

4

100.1

rays confluent with ground tissue

1

105

ray: all cells upright or square

10

108

ray: heterocellular with >4 upright cell rows (radial section) 1

110

rays with sheet cells (tangential section)

4

117

rayless

5

144

druses present

5

R1

groups of sieve tubes present

10

R3

distinct ray dilatations

3

R4

sclereids in phloem and cortex

5

R8

with crystal druses

10

P1

with medullary phloem or vascular bundles

2

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