Discussion in relation to previous studies

Detailed studies of 19 woody Gentianaceae species were performed by Carlquist (1984) and by Carlquist and Grant (2005). The xylem and phloem of Gentianaceae of a few herbaceous species is briefly described in Metcalfe and Chalk (1957; Blackstonia, Centaurium, Swertia). Jansen and Smets (1998) studied vestured pits in woody Gentianaceae.

All observations on Ixanthus correspond with those from Carlquist (1984). Metcalfe and Chalk (1957) recognized medullary phloem as a family-typical feature. The present study differs from the previous studies because earlier authors concentrated on the xylem of shrubs and dwarf shrubs. The present study concentrates on herbaceous species. Interxylary phloem as well as medullary phloem occurs frequently but is not always present. Two groups could be separated: The first is characterized by a fibrous xylem and the second by pervasive parenchyma.

Present features in relation to the number of analyzed species

61

fiber pits small and simple to minutely bordered

IAWA code

frequency

(<3 pm = libriform fibers)

11

Total number of species

25

68

fibers thin-walled

2

1

growth rings distinct and recognizable

11

69

fibers thick-walled

8

2

growth rings indistinct or absent

1

70

fibers thin- to thick-walled

7

2.1

only one ring

14

75

parenchyma absent or unrecognizable

13

4

semi-ring-porous

3

79

parenchyma paratracheal

1

5

diffuses-porous

4

79.1

parenchyma pervasive

12

9

vessels predominantly solitary

18

97

rays width predominantly 1-3 cells

1

9.1

vessels in radial multiples of 2-4 common

3

105

ray: all cells upright or square

1

10

vessels in radial multiples of 4 or more common

8

117

rayless

25

11

vessels predominantly in clusters

1

120

storied axial tissue (parenchyma, fibers,

13

vessels with simple perforation plates

23

vessels in tangential section)

4

20

intervessel pits scalariform

5

135

interxylary phloem present

4

39.1

vessel cell-wall thickness >2 pm

2

R1

groups of sieve tubes present

21

40.1

earlywood vessels: tangential diameter <20 pm

14

R2

groups of sieve tubes in tangential rows

10

40.2

earlywood vessels: tangential diameter 20-50 pm

11

R9

with crystal sand

1

50.1

100-200 vessels per mm2 in earlywood

24

R10

phloem not well structured

8

50.2

200-1000 vessels per mm2 in earlywood

1

R11

with rhaphides

1

59

vessels absent or indistinguishable from fibers

1

R14

cortex with aerenchyma

1

60.1

fibers absent

9

P1

with medullary phloem or vascular bundles

25

Detailed illustration of Fig. 18: Ixanthus viscosus, transverse section.

phloem in formation xylem in formation

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