Cucurbitaceae

Number of species, worldwide and in Europe

The cosmopolitean Cucurbitaceae family includes 118 genera with 825 species. In Europe, there are 8 genera with 14 species. This number includes cultivated species, e.g. Cucumis and Cucurbita.

Analyzed species:

Bryonia dioeca Jacq., shoot and tuber Bryonia verrucosa Ait.

Citrullus colocynthis (L.) Schrad., shoot and tuber Cucurbita maxima Duch. ex Lam., root collar Cucurbita pepo L., shoot Cucumis sativus L., shoot

Ecballium elaterinum (L.) Rich., shoot and tuber

Analyzed material

The xylem and phloem of 5 genera with 7 species are analyzed here.

Life forms analyzed:

Nanophanerophytes 0.5-4 m

Hemicryptophyte with annual, ^ liana-like shoots

Therophytes with annual, liana- 3 like shoots

Studies from other authors:

4 22

Plants analyzed from different vegetation zones:

Hill and mountain 4

Mediterranean 1

Subtropical 1

Arid 1

Cucurbita Pepo Vascular Bundle
Bryonia dioeca
Cucurbita Sativa

Cucurbita sativa

Citrullus colocynthis

Cucurbita sativa

Citrullus colocynthis

Characteristics of the xylem

The constructions of annual shoots, including those of hemi-cryptophytes, is consistent. Radially arranged bi-collateral vascular bundles surround the pith (Figs. 1-3). Vascular bundles are divided into two parts: the centripetal part consists of a centripetal phloem and a centrifugal metaxylem (Figs. 4 and 5) with distinct helical thickenings (Fig. 6). A cambium between the xylem and phloem does not exist. The external part represents a vascular bundle with a centripetal xylem, a cambium, and a centrifugal phloem (Figs. 4 and 5). Large primary rays separate vascular bundles laterally. Secondary large rays are initiated in the xylem of the vascular bundles (Fig. 5). Radial growth between vascular bundles is possible, initiated by an inter-vascular cambium (Fig. 5 and detailed illustration).

Successive cambia occurring in roots and tubers of perennial species of vascular bundles are arranged in concentric rings in Bryonia, Citrullus and Ecballium (Fig. 7). Vessels of most species are arranged solitary (Figs. 1, 2 and 7). The diameter of large vessels varies from 150-250 pm. Vessels are short and thick-walled (Fig. 8) with simple perforations.

Interxylary Phloem

Fig. 3. Long vascular bundles between un-linignifed large rays. Vessels are surrounded by lignified paratracheal and unlignified apotracheal parenchyma. A few vessels contain unlignified tylosis. 3 m-long, lying, liana-like annual shoot, geophyte with a tuber, grazed wadi, arid zone, Sahara, Libya. Citrullus colocynthis, transverse section.

Left Fig. 1. Isolated vascular bundles are embedded in parenchyma tissue. The shoot is surrounded by a band of fibers within the cortex. 2 m-long, lying, liana-like annual shoot, therophyte, garden, hill zone, Zürich, Switzerland. Cucumis sativus, transverse section.

Right Fig. 2. Isolated vascular bundles are embedded in parenchyma tissue. Bundles are separated by large, primary rays. The shoot is surrounded by a band (broken) of fibers within the cortex. The annual shoot has already formed a phellem. 1.5 m-long, lying, liana-like annual shoot, geophyte with a tuber, ruderal site, Mediterranean zone, Estremadura, Spain. Ecballium elat-erinum, transverse section.

Fig. 5. Sector of an annual shoot with a bi-collateral vascular bundle. A cambium occurs only in the external part. 2 m-long annual shoot, geophyte with a tuber, ruderal site, Mediterranean, Santa Pau, Catalonia, Spain. Bryonia dioeca, transverse section. See detailed illustration.

Fig. 3. Long vascular bundles between un-linignifed large rays. Vessels are surrounded by lignified paratracheal and unlignified apotracheal parenchyma. A few vessels contain unlignified tylosis. 3 m-long, lying, liana-like annual shoot, geophyte with a tuber, grazed wadi, arid zone, Sahara, Libya. Citrullus colocynthis, transverse section.

Fig. 4. Sector of an annual shoot with a bi-collateral vascular bundle. A cambium occurs only in the external part. 2 m-long, lying, liana-like annual shoot, therophyte, garden, hill zone, Zürich, Switzerland. Cucumis sativus, transverse section. See detailed illustration.

Fig. 5. Sector of an annual shoot with a bi-collateral vascular bundle. A cambium occurs only in the external part. 2 m-long annual shoot, geophyte with a tuber, ruderal site, Mediterranean, Santa Pau, Catalonia, Spain. Bryonia dioeca, transverse section. See detailed illustration.

Inter-vessel pits are predominantly small and round; they are arranged in opposite position in Citrullus (Fig. 8) and scalari-form in the other species (Fig. 9). Small, thin-walled, unligni-fied tylosis occur in Cucumis, Citrullus and Ecballium (Figs. 1 and 2). Fibers are absent in Cucumis sativus (Fig. 4) and thin- to thick-walled with large pits in the other species. Septate fibers have been observed in Citrullus and Cucumis (Fig. 10).

The axial parenchyma is mostly paratracheal, though it can be locally apotracheal to pervasive, e.g. in the tubers of Bryonia, Citrullus and Ecballium (Fig. 7) and it is mostly storied (Fig. 11). Rays of all species are very large (>10 cells) and un-lignified (Fig. 12). Crystals were not found in the material analyzed.

I v of metaxylem i

Bfni(

I v of metaxylem i

Bfni(

Metaxylem Vessels

Fig. 7. Tuber with concentrically arranged vascular bundles produced by successive cambia. Tuber of a geophyte, ruderal site, Mediterranean zone, Estremadura, Spain. Ecballium elaterinum, transverse section. See detailed illustration.

Fig. 6. Vessels of a metaxylem (central part of a vascular bundle) with distinct helical thickenings. 3 m-long, lying, liana-like annual shoot, geophyte with a tuber, meadow in a wadi, arid zone, Akkakus Mts., Sahara, Libya. Citrullus colocynthis, radial section.

Fig. 7. Tuber with concentrically arranged vascular bundles produced by successive cambia. Tuber of a geophyte, ruderal site, Mediterranean zone, Estremadura, Spain. Ecballium elaterinum, transverse section. See detailed illustration.

Fig. 8. Short vessels with small, round pits in opposite position. 2 m-long, lying, lianalike annual shoot, therophyte, garden, hill zone, Zürich, Switzerland. Cucumis sativus, radial section.

Fig. 6. Vessels of a metaxylem (central part of a vascular bundle) with distinct helical thickenings. 3 m-long, lying, liana-like annual shoot, geophyte with a tuber, meadow in a wadi, arid zone, Akkakus Mts., Sahara, Libya. Citrullus colocynthis, radial section.

Cucurbitaceae

ivp sf ivp sf

Left Fig. 9. Short vessels with scalariform pits. 2 m-long annual shoot, geophyte with a tuber, ruderal site, Mediterranean, Santa Pau, Catalonia, Spain. Bryonia dioeca, radial section.

Right Fig. 10. Septate fibers of the xylem with fairly large pits. 3 m-long, lying, lianalike annual shoot, geophyte with a tuber, meadow in a wadi, arid zone, Sahara, Libya. Citrullus colocynthis, radial section.

Detailed illustration of Fig. 4. Sector of an annual shoot with a bi-collateral vascular bundle. The phloem of the central part is centripetal and that of the external part is centrifugal. A cambium occurs only in the external part. 2 m-long, lying, liana-like annual shoot, therophyte, garden, hill zone, Zürich, Switzerland. Cucumis sativus, transverse section.

Cucurbita Collaterl

Detailed illustration of Fig. 5. Sector of an annual shoot with a bi-collateral vascular bundle. The phloem of the central part is centripetal and that of the external part is centrifugal. A cambium occurs only in the external part. 2 m-long annual shoot, geophyte with a tuber, ruderal site, Mediterranean, Santa Pau, Catalonia, Spain. Bryonia dioeca, transverse section.

n fD fD fD

Detailed illustration of Fig. 7. Tuber with concentrically arranged vascular bundles produced by successive cambia. Vascular bundles are arranged in two circles. Tuber of a geophyte, ruderal site, Mediterranean zone, Estremadura, Spain. Ecballium elaterinum, transverse section.

Unlignified Fibers

confluent ray storied parenchyma r pa v

Left Fig. 11. Irregularly arranged ray cells and storied axial parenchyma cells. 2 m-long annual shoot, geophyte with a tuber, ruderal site, Mediterranean, Santa Pau, Catalonia, Spain. Bryonia dioeca, tangential section.

Right Fig. 12. Large ray with thin-walled, unlignified walls. 3 m-long, lying, liana-like annual shoot, geophyte with a tuber, grazed meadow in a wadi, arid zone, Sahara, Libya. Citrullus colocynthis, tangential section.

confluent ray storied parenchyma r pa

Characteristics of the phloem and cortex

Discussion in relation to previous studies

Outside of the vascular bundles of annual shoots is the cortex. It consists of large, unlignified parenchyma cells. The cortex is divided by a ring of fibers in Cucumis, Cucurbita and Ecbal-lium (Fig. 4). Broken fiber-sclerenchyma rings are caused by dilatation (Fig. 4). Fibers are often septate (Fig. 13). The inner part of the cortex of Cucumis sativus contains a few small sieve tubes (Fig. 4). Round phloem cells with distinct sieve plates and small rectangular parenchyma cells form the phloem (Figs. 14 and 15). Dilatations occur in the bark of all perennial parts (Fig. 16). Small crystals are rare, either in irregular or in prismatic or acicular forms (Ecballium).

Zimmermann (1922) described shoots of more than 14 species from Eastern Usambara in Tanzania and Carlquist (1991) characterized 4 woody species from tropical and arid regions. Stem cross-sections of a few Cucurbitaceae species, including Ecballium elaterinum and Bryonia dioeca, are given by Metcalfe and Chalk (1955). An instructive text by Evert (2007) explains a drawing and a photograph of Cucurbita maxima and C. pepo showing an annual stem with bi-collateral bundles. The occurrence of bi-collateral vascular bundles in annual shoots and collateral bundles in parts produced by successive cambia are unique to the stem construction of all anatomically known Cucurbitaceae species (Carlquist (1991), Evert (2007), Metcalfe and Chalk (1955) and Zimmermann (1922)).

50 Mm sf

Cucurbitaceae

sieve plates v sieve plates

Left Fig. 13. Septate fibers of the ring within the cortex (see Fig. 1). 2 m-long, lying, liana-like annual shoot, therophyte, garden, hill zone, Zürich, Switzerland. Cucumis sa-tivus, radial section.

Right Fig. 14. Phloem with round sieve tubes and square and irregular parenchyma cells. Red cell contents highlight sieve plates. 2 m-long, lying, liana-like annual shoot, hemicryptophyte, banana plantation, subtropical climate, Tenerife, Canary Islands. Bryonia verrucosa, transverse section.

sieve plate

Left Fig. 15. Sieve plates in sieve tubes. 2 m-long annual shoot, geophyte with a tuber, ruderal site, Mediterranean, Santa Pau, Catalonia, Spain. Bryonia dioeca, transverse section.

Right Fig. 16. Phloem with large dilatations. Bark, 1.5 m-long, lying, liana-like annual shoot, geophyte with a tuber, rud-eral site, Mediterranean zone, Estremadura, Spain. Ecballium elaterinum, transverse section.

sieve plate

Present features in relation to the number of analyzed specimens

79

parenchyma paratracheal

6

IAWA code

frequency

79.1

parenchyma pervasive

9

Total number of specimens

99

rays commonly >10-seriate

10

(7 species; Bryonia dioeca, Citrullus colocynthis and

99.1

vascular-bundle form remaining

4

Ecballium elaterinum shoot and tuber)

10

99.2

stem lobed

0

1 growth rings distinct and recognizable

2

100.1 rays confluent with ground tissue

4

2.1 only one ring

8

100.2

rays not visible in polarized light

9

9 vessels predominantly solitary

10

103

rays of two distinct sizes (tangential section)

6

13 vessels with simple perforation plates

10

105

ray: all cells upright or square

10

20 intervessel pits scalariform

6

110

rays with sheet cells (tangential section)

2

21 intervessel pits opposite

7

120

storied axial tissue (parenchyma, fibers and vessels

39.1 vessel cell-wall thickness >2 pm

8

in tangential section)

3

41 earlywood vessels: tangential diameter 50-100 pm

3

133.1

successive cambia, concentrically arranged

42 earlywood vessels: tangential diameter 100-200 pm

7

single vascular bundles

1

50 <100 vessels per mm2 in earlywood

9

134

successive cambia, diffuse = foraminate

2

56 tylosis with thin walls

6

134.1

conjunctive tissue thin-walled

3

60.1 fibers absent

4

135

interxylary phloem present

2

61 fiber pits small and simple to minutely bordered

R1

groups of sieve tubes present

1

(<3 pm = libriform fibers)

2

R3

distinct ray dilatations

9

62 fiber pits large and distinctly bordered

R4

sclereids in phloem and cortex

4

(>3 pm = fiber tracheids)

4

R7

with prismatic crystals

1

65 septate fibers present

2

R10

phloem not well structured

10

70 fibers thin- to thick-walled

6

R11

with rhaphides

2

76 parenchyma apotracheal, diffuse and in aggregates

3

P1

with medullary phloem or vascular bundles

10

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