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Structure and Development |
2Botany, The University of New England, Armidale, NSW, 2351, Australia;and 3National Herbarium of NSW, Royal Botanic Gardens Sydney, Mrs Macquaries Road, Sydney, NSW, 2000, Australia
Received for publication March 27, 2003. Accepted for publication July 3, 2003.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSTERMINOLOGYRESULTSDISCUSSIONLITERATURE CITED |
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Key Words: Cyperaceae • monopodial • prophyll • rachilla • Rhynchosporeae • Schoeneae • spikelet • sympodial
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSTERMINOLOGYRESULTSDISCUSSIONLITERATURE CITED |
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), and consequently to different classifications. For example, the Schoeneae, previously commonly named Rhynchosporeae (Bentham, 1883
; Koyama, 1961
; Schultze-Motel, 1964
; Hooper, 1973
; see Zhang, 2002
, for a review of Schoeneae) was placed (as Rhynchosporeae) in the same subfamily as Scirpeae by Bentham (1883)
, but Pax (1887)
removed the tribe to the subfamily Caricoideae because of the sympodial structure of the spikelet. Later, Schultze-Motel (1964)
considered the spikelets of the tribes Rhynchosporeae, Scirpeae, and Cypereae to be sympodial and put them in the same subfamily, while Eiten (1976)
insisted all these tribes had racemosely branched spikelets. The crucial dispute is whether spikelet structure is cymose (or a rhipidium, which is a sympodial structure) or racemose (a monopodial structure). Currently most literature, including floras, treats spikelets in Schoeneae (or Rhynchosporeae) as monopodial structures (e.g., Haines and Lye, 1983
; Kukkonen, 1986
; Wilson, 1993
).
Since Wilhelm Hofmeister (1824–1877), it has been customary to classify inflorescences as racemes (racemose inflorescences) or as cymes (cymose inflorescences) (Weberling, 1989
). A raceme is defined as an inflorescence characterized by a monopodial axis on which flowers are lateral. The cyme is constructed sympodially, and flowers are terminal (Guédès, 1979
; Weberling, 1989
; Bell, 1991
). The cymose inflorescence can be subdivided into a monochasium, dichasium, or pleiochasium. The monochasium can be further characterized as a rhipidium, drepanium, cincinnus, or bostryx (Bell, 1991
). A rhipidium is constructed sympodially, with alternate lateral branches, each of which terminates with a flower (Fig. 1a–c). This type of inflorescence is also called a scorpioid cyme (Radford et al., 1974
; Eiten, 1976
).
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, 1887
); this interpretation was supported by some later authors (Celakovsk
, 1887
; Hamlin, 1956
; Kern, 1962
; Schultze-Motel, 1964
). They interpreted the spikelet structure of this tribe as follows: the proximal flower terminates the main axis of the spikelet, and the second flower terminates a secondary axis arising from the axil of the uppermost glume on the main axis, with the secondary axis bearing only one glume, from which further branching may proceed (Fig. 1a–c). In this case, the flowers are terminal, not axillary to a glume; the glume, which apparently subtends a flower, really subtends the new branch forming the next rachilla internode. This view was also supported for Rhynchospora macrostachya Torr. ex A. Gray (Blaser, 1941
), Cladium (Mora, 1960
; Richards, 2002
), Schoenus (Mora, 1960
), the Schoeneae of Clarke (1908)
(Schönland, 1922
), Trianoptiles (Levyns, 1943
; Phillips, 1951
), Epischoenus (Leighton et al., 1947
; Levyns, 1959
), and Costularia (Browning, 1994
). In this view, Pax (1886
, 1887
), Celakovsk (1887)
, and Mora (1960)
identified the distal bracts as prophylls subtending the axillary continuation axis of the sympodial spikelet, while Schönland (1922)
, Blaser (1941)
, Levyns (1943
, 1959)
, Leighton et al. (1947)
, Phillips (1951)
, Hamlin (1956)
, Schultze-Motel (1964)
, and Kern (1962)
did not mention any prophyll structure in their description of sympodial spikelet structure.
On the other hand, the interpretation of spikelet structure in Schoeneae (or Rhynchosporeae) as racemose with a monopodial rachilla is preferred by many authors (Holttum, 1948
; Koyama, 1961
; Haines, 1967
; Raynal, 1971
; Eiten, 1976
; Haines and Lye, 1977
; Kukkonen, 1986
; Browning and Guthrie, 1994
). They considered the spikelet structure of this tribe to be as follows: the flowers are lateral (they do not terminate the rachilla, which continues growing to produce further glumes and flowers), and each flower is situated in the axil of the subtending glume (i.e., between the glume and the rachilla) (Fig. 1d). These authors used different evidence to support this view. Holttum (1948
, p. 535) stated that the two-keeled prophyll of Asterochaete, Elynanthus, and Gahnia, supposed by Pax to accompany the second flower, does not exist: "Such a prophyll is normally present at the base of every branch in Cyperaceae and would be clear indication that branching had occurred ... and in the absence of a prophyll there seems no evidence that branching occurred." Koyama (1961)
proposed Rhynchosporoid-type spikelets (a reduced Scirpoid spikelet structure) for Rhynchosporeae (= Schoeneae), and the arrangement of glumes in the Scirpoid spikelet supported this interpretation as a racemose structure. The explanation of Haines (1967)
was not based on the absence of prophylls. He explained that each flower was enwrapped by the winglike margins of the glume above in Rhynchospora, Cladium, and Schoenus. Haines and Lye (1977)
also held the same view in Trianoptiles. Eiten (1976
, pp. 87–88) supported the interpretation of the spikelet structure as racemose by her "preliminary observation that there is no anatomical evidence for recaulescence and therefore sympodiality," i.e., "the glumes are really on the same side of the rachilla as their flowers, appearing to subtend them." Kukkonen (1986
, p. 118) supported the view of a monopodial spikelet structure in Rhynchosporeae and argued that "in the inflorescence of Schoenus ferrugineus the glume extends to the opposite side of the inflorescence axis, between the glume and flower, and embraces the flower as well as the axis." Browning and Guthrie (1994
, p. 151) would not accept the spikelet structure in Carpha as cymose despite finding that spikelets in Carpha had the same structure as described by Levyns for the sympodial spikelet structure of Trianoptiles and Epischoenus. They interpreted "the floret as occupying considerable space and appearing pseudo-terminal, making further rachilla growth possible only as a slightly elongated extension that must curve to accommodate the expanding floret with its maturing fruit."
How to distinguish the two types of spikelets in Schoeneae is a controversial issue. Mora (1960)
stated that the decisive indication for cymose structure (the rachilla is sympodial) is a terminal flower at the apex of the rachilla. Racemose structure (the rachilla is monopodial) lacks this terminal flower. Eiten (1976
, p. 87) pointed out "An apparent terminal position of a flower in the Cyperaceae is no indication that it really is so; rather, it may well be pseudoterminal, that is, lateral."
Browning and Gordon-Gray (1995b)
suggested that a more convincing explanation of spikelet structure should be sought. Based on their observations on Rhynchospora gracillima subsp. subquadrata, they considered the flowers not to be axillary to the glumes, yet they considered that an interpretation of sympodial construction for the spikelet was not acceptable. However, they did not pursue this issue further.
In this study, we address these controversial issues through a comparative study of spikelet structure in tribe Schoeneae. Our aims are to document and clearly describe spikelet structure in Schoeneae and to resolve differing interpretations and clarify relevant concepts of spikelet structure in Schoeneae.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSTERMINOLOGYRESULTSDISCUSSIONLITERATURE CITED |
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; Goetghebeur, 1998
; see Zhang, 2002
, for a review of Schoeneae). Specimens with many spikelets were chosen for examination (Appendix, see Supplemental Data accompanying the online version of this article). The number of spikelets examined varied from two to several for each specimen until the spikelet structure of the specimen could be unambiguously determined. The herbarium specimens were from the following herbaria: B, BM, BOL, CANB, EA, HO, K, MEL, MO, NE, NSW, NU, NY, P, and PRE. Herbaria abbreviations follow Holmgren and Holmgren (1990)
. Fresh material was collected and fixed in FAA or FPA (Prakash, 1986
) in the field in Australia (Kosciuszko National Park, the south coast of New South Wales, and National Parks in the New England region of NSW, and Tasmania). After a few weeks, material was transferred to Kew Mix (1% glycerine in 70% ethanol) for long-term preservation. Vouchers have been lodged at NE and NSW and replicate specimens distributed widely.
Dissection
Glumes were carefully removed from the proximal to the distal end of a spikelet under a Stemi 2000 Zeiss (Jena, Germany) or a Leica MZ75 (Heerbrugg, Switzerland) dissecting microscope. Spikelets from herbarium specimens were observed either directly or after softening in boiling water with a drop of detergent. Some dissections were stained with toluidine blue to assist in viewing.
Scanning electron microscopy
Spikelets from herbarium specimens, after removal of selected glumes and fruits, were mounted on stubs with double-sided tape, sputter-coated with gold using a Polaron E5100 coating unit (Watford, England), and viewed with a JEOL JSM-5800LV (Tokyo, Japan) scanning electron microscope (SEM) at 15 kV. For species with rachillas that break easily if dissected directly, the spikelets were hydrated by boiling in water with a drop of detergent. After dissection, they were dehydrated using an ethanol dehydration series and mounted on stubs. Pickled material, after removal of selected glumes and fruits, was dehydrated using the same alcohol dehydration series, and then mounted on stubs. The SEM images were scanned to disk at high resolution, and electronic plates were constructed using Adobe Photoshop and Illustrator (San Jose, California, USA).
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TERMINOLOGY |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSTERMINOLOGYRESULTSDISCUSSIONLITERATURE CITED |
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; Eiten, 1976
; Weberling, 1989
; Harris and Harris, 1994
; Kukkonen, 1994
). As discussed earlier, the spikelet of Schoeneae has been interpreted as monopodial by some authors (Holttum, 1948
; Koyama, 1961
; Haines, 1967
; Raynal, 1971
; Eiten, 1976
; Haines and Lye, 1977
; Kukkonen, 1986
) and as sympodial by others (Pax, 1886
, 1887
; Celakovsk, 1887
; Hamlin, 1956
; Mora, 1960
; Kern, 1962
; Schultze-Motel, 1964
). When the spikelet in Schoeneae is interpreted as a monopodial structure, it is a true spikelet as defined, but does not fit the definition when the spikelet is interpreted as a sympodial structure. However, most authors who interpreted the Schoeneae spikelet to be a sympodial structure still called it a spikelet (Levyns, 1943
, 1959
; Leighton et al., 1947
; Phillips, 1951
; Hamlin, 1956
; Kern, 1962
, 1974
; Browning, 1994
), although some used "partial inflorescence," "Scheinährchen" (pseudospikelet), or "spikelet" (in quotes) (Pax, 1886
, 1887
; Celakovsk, 1887
; Schönland, 1922
; Blaser, 1941
; Schultze-Motel, 1964
). In this study, a spikelet is defined as the smallest inflorescence unit that is easily identified by the unaided eye, including both sympodial- and monopodial-branching structures. Spikelets with sympodial branching are called sympodial spikelets, and spikelets with monopodial branching are called monopodial spikelets.
Rachilla and "rachilla"
A rachilla is defined as "a diminutive or secondary axis, or rachis" (Lawrence, 1951
, p. 767). In this study, monopodial spikelets have a single (simple) rachilla (Fig. 1d); sympodial spikelets have successive axes, resulting in a "rachilla" consisting of a succession of single rachillas or axes (Fig. 1a–c).
Glume
Most authors have used the term "glume" for parts of the spikelet in Cyperaceae, but Haines and Lye (1983)
used both "glume" and "scale" to describe the spikelets of Carpha and its relatives, and Bruhl et al. (1992)
and Bruhl (1995)
used "floral bracts" in describing the spikelet in Cyperaceae. In this study "glume" is still used, in accordance with traditional usage in this family. To avoid including the spikelet bract as a glume (see Bruhl, 1995
; Goetghebeur, 1998
), "glume" in this study is defined as a small bract in the spikelet, including any proximal sterile and any distal empty ones, but not the bract subtending the spikelet.
Fertile glume
A glume that directly encloses or partly encloses an adjacent male, female, or bisexual flower, as indicated in Figs. 2–6.
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Basal shape of glumes
Most species observed have glumes with a typically slightly curved, more or less truncate base (see Fig. 4b). However, the fertile glumes in some species of Schoenus and in Ptilothrix deusta have an arch-shaped base (see Figs. 2b, c, 3c, 4c, 6; also see Browning and Gordon-Gray, 1995a
, fig. 5).
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Prophyll
The monocot prophyll, as seen in Cyperaceae, is defined as a foliar organ with two more or less equally developed main vascular bundles each with its own keel, rather than having the single main bundle and single keel seen in other bracts and glumes. When present, it is the first foliar organ on a lateral axis, that is, proximal on the lateral shoot, and it is adaxial to the lateral shoot (Haines, 1967
; Kern, 1974
; Haines and Lye, 1983
; Bruhl et al., 1992
; Kukkonen, 1994
).
Bisexual flower
This refers to a flower in which both pistil and stamens develop.
Male flower
This refers to a flower with stamens but without a developed pistil.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSTERMINOLOGYRESULTSDISCUSSIONLITERATURE CITED |
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Whether spikelets have an empty uppermost glume or not is also variable within some species (Carpha angustissima, C. borbonica, C. capitellata, C. cf. nitens, C. eminii, C. nitens, C. perrieri, C. schlechteri, C. schoenoides, Cyathochaeta clandestina, Cyathocoma hexandra, Schoenoides oligocephalus, Schoenus maschalinus, S. rhynchosporoides, Tetraria capillaris and Tricostularia pauciflora) (Fig. 7; Appendix, see Supplemental Data accompanying the online version of this article), and even on the same plant: Carpha angustissima (P 199386), C. borbonica (I. B. Balfour s.n.), C. capitellata (Drège 1840), C. cf. nitens (I. B. Balfour s.n.), C. nitens (M. J. E. Coode 4186; C. Barclay 1920), C. perrieri (H. Humbert 6146), and Cyathocoma hexandra (B. Sonnenberg 477) (Fig. 7; Appendix, see Supplemental Data accompanying the online version of this article).
The proximal portion of the "rachilla" (the part that carries the sterile glumes) is straight and stouter than the remainder of the "rachilla" (Figs. 2, 3d, 4a, d, e, 5 and 6c, d). The distal portion (the part that carries fertile glumes and the empty uppermost glume) is more or less curved (zigzag) except for any node on which a male flower occurs. If a node carries a male flower, the internode above that node lies in the same direction as the internode below it (Fig. 7h, o, s), which occurs consistently in Capeobolus brevicaulis, Costularia pilisepala, Gahnia sieberiana, Gymnoschoenus sphaerocephalus, and Schoenus paludosus, and occasionally in some specimens of other species: Carpha schlechteri (R. Schlechter 10010; M. R. Levyns 8098; J. Browning 823), Cyathochaeta avenacea (NSW 462122), C. clandestina (NE 66021), C. diandra (NE 66023, NE 72997, NSW 462124) (Fig. 7h, o, s; Appendix, see Supplemental Data accompanying the online version of this article).
In some species, the "rachilla" elongates above the nodes on which the bisexual flowers occur (Fig. 7c, e, g, j, k, l, n, o, q, s, u, v; Appendix, see Supplemental Data accompanying the online version of this article). These internodes are much longer than the lower internodes associated with the proximal sterile glumes. Such elongated "rachilla" internodes exist in Carpha angustissima, C. borbonica, C. bracteosa (Fig. 4d, e), C. capitellata (Fig. 5a), C. filifolia, C. glomerata, C. nitens, C. perrieri, C. schlechteri (B. Sonnenberg 458), Ptilothrix deusta (Figs. 3d, 4a), Schoenus andinus (Fig. 2d), S. antarcticus, some specimens of S. maschalinus (NSW 422022, NSW 247917), S. calostachyus, S. brevifolius (Fig. 6c, d), Trianoptiles capensis, T. stipitata, and T. solitaria. In other species, the "rachilla" does not elongate at all; internodes above the fertile glume(s) have almost the same length as internodes above the proximal sterile glume(s) (Figs. 2a, 5b–d, 7a, b, d, f, h, i, m, p, r, t; Appendix, see Supplemental Data accompanying the online version of this article).
Spikelet structures of some species of Schoenus (Schoenus andinus, S. antarcticus, S. brevifolius, S. calostachyus, and some specimens of S. maschalinus) and of Ptilothrix deusta are special. The proximal part of the "rachilla" (which carries sterile glumes), as in other species of Schoeneae examined here, is straight, and the glumes on it have a curved, more or less truncate base (Figs. 3a, b, 4b). However, the distal parts (which carry fertile glumes) elongate to produce a strongly zigzag "rachilla," and result in inclined nodes and irregular shaped internodes. In turn, each inclined node results in the arch-shaped base of the glume that initiates at that node and subtends the next axillary internode and surrounds its flower on the opposite side of that internode (Figs. 2b–d, 3c, d, 4a, c, 6).
In spikelets of some species, the base of each fertile glume is adnate to the "rachilla" above it (Fig. 7e, k, l, q; Appendix, see Supplemental Data accompanying the online version of this article). This occurs in Carpha angustissima, C. borbonica, C. bracteosa (Fig. 4d, e), C. capitellata (Fig. 5a), C. filifolia, C. glomerata, C. nitens, C. perrieri, C. schlechteri (B. Sonnenberg 458), Trianoptiles capensis (BOL 63222), and T. solitaria.
A prophyll was seen in only a few of the spikelets observed. Only Costularia elongata, Cyathocoma hexandra (except R. Schlechter 10280, and C. J. Ward 1060; both have a bract with two obscure veins that seems like a prophyll), and Schoenoides oligocephalus (HO 47874, HO 60127 and HO 102690) have an obvious two-veined prophyll distal to the proximal fertile glume in the spikelet (Fig. 7d, i, p; Appendix, see Supplemental Data accompanying the online version of this article). The glume distal to the proximal fertile glume in the spikelet in Carpha schoenoides (MO 2150322; MO 1626156; D. M. Moore 1835; W. J. Eyerdam 10586A), Tricostularia pauciflora, Trianoptiles capensis, T. stipitata, and T. solitaria has two keels and two obscure veins, which we interpret as possibly a prophyll. We list two possible kinds of spikelet structure for these specimens in the Appendix (see Supplemental Data accompanying the online version of this article). If the distal organ is not interpreted as a prophyll, the first spikelet structure listed in each case would be the appropriate one; otherwise, the second structure is appropriate (Fig. 7d, i, j, l, p; Appendix, see Supplemental Data accompanying the online version of this article). All other species have no trace of a two-veined prophyll in the spikelets, in which all the glume(s) distal to the proximal fertile glume have only one keel (one vein) or are not keeled (no vein) at all. Moreover, no prophylls were found in any part of the inflorescences in most species of Schoeneae examined, such as in species of Schoenus and Carpha (except C. schoenoides).
In summary, the spikelets of Schoeneae develop acropetally. The "rachilla" is formed sympodially, that is, each flower is terminal on a "rachilla" internode and surrounded by its subtending glume. The next "rachilla" internode is axillary to the proximal fertile glume and is produced between that glume and its flower. The "rachilla" may then produce another terminal flower and the process may be repeated. The flower does not appear axillary to its glume but opposite it, with the "rachilla" internode between the two. Spikelets in Schoeneae can vary in the following ways:
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSTERMINOLOGYRESULTSDISCUSSIONLITERATURE CITED |
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, Eiten (1976)
, Guédès (1979)
, and Bell (1991)
. The flowers in the spikelets have a very contracted stalk or are sessile (Figs. 2– 6). All types of spikelet structures in Schoeneae (Fig. 7) can be derived simply by changing the flower stalks to short or very short from a standard rhipidium (Fig. 1a–c). Monopodial spikelets in Schoeneae, as described by most of the current literature, including floras, were not found in this study.
Spikelet structures in Schoeneae are consistently sympodial rather than monopodial. Because they have strongly zigzag, elongated "rachillas" in the fertile distal part of their spikelets, species of Schoenus have often been chosen as an example to illustrate spikelet structure for Schoeneae (or Rhynchosporeae) in previous studies. Haines (1967)
illustrated how each flower was enclosed by the winglike margins of the glume above in Schoenus and other genera. Kukkonen (1986
, p. 118) also argued that "in the inflorescence of Schoenus ferrugineus the glume extends to the opposite side of the inflorescence axis, between the glume and flower, and embraces the flower as well as the axis." The arch-shaped base of fertile glumes in some species of Schoenus has also been described as decurrent on the rachilla (Holttum, 1948
; Kern, 1974
). These descriptions are contradicted by the fact that the fertile glume is on the opposite side of the "rachilla" from the point of attachment of its flower and subtends a new branch forming the next "rachilla" internode. The actual line of glume attachment to the "rachilla" is below, or at least at the same level as, the point of attachment of its flower on the opposite side of the "rachilla" (Figs. 2, 3, 4a, d, e, 5, 6 and 7). In species of Schoenus, there are two types of "rachilla." In one type, the "rachilla" above the fertile glumes does not elongate (Figs. 7a, b, f, m, o, t; Appendix, see Supplemental Data accompanying the online version of this article), for example in S. rhynchosporoides (Fig. 5b–d). Here the "rachilla" internode above a fertile glume is between the fertile glume and its flower, and the lines of attachment of the two fertile glumes are lower than the point of attachment of the flowers subtended by them respectively. The other type is where the "rachilla" internode above a fertile glume elongates strongly (Fig. 7c, g, n, u, v; Appendix, see Supplemental Data accompanying the online version of this article) and fertile nodes are inclined, such as in S. andinus (Fig. 2b–d) and S. brevifolius (Fig. 6). The shape of the inclined nodes leads to the glumes initiated on them having an arch-shaped base. The lowest point of the line of glume attachment to the "rachilla" is below, or at least at the same level as, the point of attachment of its flower on the opposite side of the "rachilla." Another genus that has fertile glumes with an arch-shaped base is the monotypic genus Ptilothrix. In P. deusta, the "rachilla" is elongated above the fertile glume, the fertile nodes are inclined, and the glumes that are attached to these inclined nodes have an arch-shaped base (Figs. 3c, 4c). The lowest point of the line of glume attachment to the "rachilla" is below the point of attachment of its flower on the opposite side of the "rachilla" (Figs. 3c, d, 4a). All the other genera had the line of glume attachment to the "rachilla" below the point of attachment of its flower on the opposite side of the "rachilla" (Figs. 2a, 4d, e, 5a, 7). These results are supported by the independently derived illustrations of Celakovsk (1887)
for Schoenus, Blaser (1941)
for Rhynchospora macrostachya, Levyns (1943)
for Trianoptiles, Leighton et al. (1947)
and Levyns (1959)
for Epischoenus, Browning (1994)
for Costularia, Browning and Guthrie (1994)
for Carpha, and Browning and Gordon-Gray (1995a
, b
) for Epischoenus, Schoenus, and Rhynchospora gracillima subsp. subquadrata, and by the developmental work of Mora (1960)
for Cladium and Schoenus, and Richards (2002)
for Cladium.
Browning and Guthrie (1994)
and Browning and Gordon-Gray (1995a
, b
), however, could not accept the spikelet structure as cymose, although their diagram (1994, fig. 1A, E) clearly shows that the spikelet structure is cymose and its "rachilla" is best interpreted as sympodial. Browning and Gordon-Gray (1995a
, p. 150) also concluded that flowers in Epischoenus and Schoenus are nonaxillary, and wondered "if the bisexual floret does indeed terminate the spikelet rachilla, why should the functionally male florets in Epischoenus appear so markedly laterally placed in relation to the rachilla, and why should the rachilla appear to continue growth directly, without evidence of growth of a branch of succeeding order?" Later Browning and Gordon-Gray (1995b)
suggested that a more convincing explanation should be sought because they considered the flowers not to be axillary to the glumes, but that an interpretation of sympodial construction for the spikelet was not acceptable for Rhynchospora gracillima subsp. subquadrata.
If each glume is positioned on the opposite side of the "rachilla" from the point of attachment of its flower (Fig. 1a–c), the spikelet structure is best interpreted as sympodial. In a monopodial structure, the glumes are on the same side of the rachilla as the points of attachment of their flowers (Fig. 1d) (Eiten, 1976
). If the flower is not axillary to the glume, it must be terminal to the "rachilla," and the "rachilla" develops sympodially. The illustrations of Browning (1994
, p. 654, figs. B, C, D) for Costularia, Browning and Guthrie (1994
, p. 150, fig. 1) for Carpha, and Browning and Gordon-Gray (1995a
, p. 151, fig. 6; 1995b
, p. 321, figs. 2, 3) for Epischoenus, Schoenus, and Rhynchospora clearly show that each flower is not axillary to its glume; each fertile glume is on the opposite side of the "rachilla" from the point of attachment of its flower and subtends a new branch forming the next "rachilla" internode. Thus, the spikelets have a sympodial structure, and the bisexual flowers and the male flowers terminate the spikelet "rachilla" internodes. If the spikelets were racemose, flowers should be in the axils of glumes and between the glume and axis, i.e., the flowers should be on the same side of the rachilla as the glumes subtending them (Fig. 1d). However, they are not. A spikelet must be constructed in one of two ways, i.e., either monopodial or sympodial, depending on whether the position of each new distal shoot unit is apical or axillary (Bell, 1991
).
In Schoeneae, when a proximal male flower is present, the internode above this male flower lies in the same direction as the internode below it (Fig. 7h, o, s). It is not difficult to understand why sympodial structure can have some flowers appearing so markedly laterally placed in relation to the "rachilla." In some sympodial inflorescences, the consecutive branches are constructed more or less in the direction of the main axis, and their respective terminal flowers are pushed to the side, creating a superficial impression of a monopodial axis with flowers developing from an axillary position (Weberling, 1989
). Bell (1991)
gave Fremontodendron californica as an example of this phenomenon.
Browning and Gordon-Gray (1995a
, p. 150) explained the arch-shaped base of fertile glumes in some species of Schoenus as resulting from "drying of the rachilla following fruit maturation [so that] there is tearing away from the main body of the glume, of the portion that was adnate to the rachilla, causing the arch-shaped hole and leaving the two lateral strips attached to the node from which the glume developed." However, no evidence of glumes being adnate to the "rachilla" from which they originate and subsequently causing their arch-shaped bases was found in species of Schoenus observed in the present study. The nodes associated with the flowers that are functionally bisexual incline in some species of Schoenus, and the glumes growing on them have an obvious demarcation line from the "rachilla" (Figs. 2c, 6). That these glumes have an arch-shaped base is only because they grow on the inclined nodes and match the shape of the node. This is also seen in Ptilothrix (Figs. 3c, d, 4a, c).
In some species in tribe Schoeneae, the basal part of the fertile glumes is adnate to the next internode (Figs. 4d, e, 5a, 7e, k, l, q). This was previously observed by Levyns (1943)
in Trianoptiles solitaria. That the basal part of the fertile glumes is adnate to the next internode is evidence that the new branch (or next "rachilla" internode) arises in the axil of the glume (i.e., it is sympodial in structure).
Using prophyll presence or absence to determine inflorescence type is not reliable. Spikelets of some species have a prophyll and/or prophyll-like structures distal to the proximal fertile glume (Fig. 7d, i, j, l, p; Appendix, see Supplemental Data accompanying the online version of this article). This result is supported by previous findings of Pax (1886)
in Elynanthus, Mora (1960)
in Cladium, and Browning (1994)
in Costularia. Such a prophyll was also reported in Asterochaete (Pax, 1886
), Gahnia (Pax, 1886
), and Schoenus (Celakovsk, 1887
; Pax, 1887
; Mora, 1960
), but it was not found in our sample of Asterochaete (= Carpha p.p.), Gahnia or Schoenus in this study. No prophylls were found in spikelets of many species of Schoeneae (Fig. 7; Appendix, see Supplemental Data accompanying the online version of this article) in this study. Sometimes prophylls do not exist anywhere in the whole inflorescence. This has been previously reported by Haines (1967)
and Bruhl (1995)
. Holttum (1948)
considered the existence of a prophyll as a criterion to judge whether branching occurred. This opinion cannot be accepted due to the following points. Firstly, the prophyll is highly reduced in spikelets and inflorescences of some genera in Cyperaceae. Many species in Schoeneae do not have prophylls in the spikelets (Fig. 7; Appendix, see Supplemental Data accompanying the online version of this article) although their spikelets are sympodial in structure. Secondly, Blaser (1944)
indicated that "prophyll" is only a leaf with various modifications and occasionally distinguished by its apparent position, and the extreme reduction and specialization of all organs of leaf-rank in inflorescences makes the distinction of prophylls and bracts difficult or impossible. In fact, it is obvious that to distinguish a two-veined prophyll from a glume does not help to determine spikelet structure at all in Schoeneae.
Mora (1960)
stated that the decisive indication for cymose structure (sympodial) or racemose structure (monopodial) is whether the spikelet has a terminal flower at its apex or not, respectively. This was applied by Browning (1994)
. However, the results of this study show that this criterion is not reliable for deciding spikelet types and flower position (lateral or terminal) on the rachilla/"rachilla." From Figs. 2a, d, 4a, d, e, 5a, d, and 7, it is apparent that these "rachillas" are sympodial and flowers are terminal, regardless of whether the "rachilla" has a terminal flower at its apex or not. In Schoeneae the spikelets develop acropetally. Sometimes in a species and even in the same plant, some spikelets have an empty uppermost glume while others do not (Fig. 7; Appendix, see Supplemental Data accompanying the online version of this article). So whether an apical flower is present or not cannot be used to decide whether the spikelet is sympodial or monopodial.
For the inflorescence whose monopodial or sympodial nature is not obvious, careful scrutiny of the relative position of flowers, bracts, and axis is necessary to judge inflorescence type (Bell, 1991
). This is the case in the Cyperaceae where the inflorescence units (spikelets) are extremely contracted. If each glume is on the opposite side of the axis from the point of attachment of its flower (Fig. 1a–c), the spikelet structure is best interpreted as sympodial. If the glumes are on the same side of the axis as the points of attachment of their flowers, the spikelet structure is monopodial (Fig. 1d) (Eiten, 1976
).
Because of the extremely contracted spikelet rachilla/"rachilla" in Cyperaceae, the same controversial issues regarding spikelet structure also exist in other tribes. For example, Eiten (1976)
considered the spikelet of tribes Cypereae and Scirpeae had a racemose structure, while Schultze-Motel (1964)
thought their spikelets were cymose. Kern (1974
, p. 446) once wrote "the structure of the spikelets is in all Cyperaceae probably sympodial," while other authors (Raynal, 1971
; Eiten, 1976
; Haines and Lye, 1983
; Goetghebeur, 1998
) held different views. Therefore, spikelet structure in other tribes of Cyperaceae needs to be reinvestigated before any definitive statement can be made about spikelet structure in the whole family.
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FOOTNOTES |
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4 Current address: Centre for Plant Biodiversity Research, Plant Industry, CSIRO, GPO Box 1600, Canberra, ACT 2601, Australia
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LITERATURE CITED |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSTERMINOLOGYRESULTSDISCUSSIONLITERATURE CITED |
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