Lophopyxis
Description
Scandent or liana-like shrubs or small trees, with interxylary bast elements, watch-spring tendrils (modified leaves or subtending leaves of inflorescences), and umbrella-like branching.
Leaves spiral, simple, serrulate to crenulate, stipulate.
Flowers small, regular, monoecious, in glomerules on the branches of loose axillary panicles.
Sepals 5, vaJvate, shortly united basally, persistent.
Petals 5(-6), much smaller than the sepals, free.
Stamens 5(-6), opposite to the sepals, with filiform filaments and subglobose introrse, almost basifixed anthers, alternating with 5(-6) oppositipetalous cordate glands, these in the ♂ ± adnate to the subtending petal, and in the ♀ ± concrescent into a 5(-6)-lobed disk (the glands or lobes opposite the ovary cells);
Ovary superior, conical, shallowly 5-ribbed, 5(-4)-celled, with 5(-4) sessile subulate stigmas;
Fruit obovoid or ellipsoid, indehiscent, fusiform, 1-locular, 1-seeded, with 5 broad stramineous wings.
Seed oblong, with endosperm;
Distribution
Asia-Tropical, Melanesia present, Micronesia present
Monotypic, in Malesia, Melanesia, and Micronesia. .
Anatomy
Anomalous secondary growth: .
The young stem has five ribs with a continuous xylem cylinder enclosing a pentagonal pith with a central portion of thick-walled parenchyma cells and a marginal area of thin-walled cells, erroneously referred to by ENGLER (l.c.) as intraxylary phloem. This thin-walled tissue may become caducous, at least in herbarium specimens. Between the ribs the secondary xylem has numerous vessels; in the ribs the vessels are narrower and scarcer. Vessel perforations are simple. Through anomalous activity of the cambium, 5 phloem strands become enclosed within xylem in the young shoot. Later interxylary phloem is formed as continuous bands alternating with secondary xylem. The phloem is stratified into soft and fibrous portions. Axial xylem parenchyma is scarce and paratracheal (only seen in young twigs). The ground tissue of the xylem is composed of fibres with numerous minutely bordered pits. Rays vary from 1-6-seriate in the young stem. The outer phloem is surrounded by a cylinder of fibres and stone cells. Cork arises in the layer below the epidermis.
The anatomy of the leaf has hitherto never been described. The petiole shows a strongly incurved arc of separate vascular bundles and two additional latero-dorsal bundles as seen in transverse section through the distal end. The vascular system forms a closed flattened cylinder in the midrib. The stomata, confined to the abaxial surface, are paracytic. Crystals are present as solitary rhomboids and clusters. The hairs are unicellular.
To evaluate the taxonomic significance of the vegetative anatomy of Lophopyxis with regard to the affinities of the genus more research is still needed. The only straightforward conclusion to be drawn at present is that Lophopyxis is anatomically entirely different from Gouania (Rhamnaceae), to which AIRY SHAW (in Willis Dict. ed. 7, 1966, 668) related it. Gouania differs e.g. in having anomocytic stomata, styloids, unlignified perivascular fibres and exclusively narrow rays. Dr. C. R. METCALFE (Kew) kindly put slides and anatomical information of Lophopyxis and Gouania at my disposal. — P. BAAS.
The young stem has five ribs with a continuous xylem cylinder enclosing a pentagonal pith with a central portion of thick-walled parenchyma cells and a marginal area of thin-walled cells, erroneously referred to by ENGLER (l.c.) as intraxylary phloem. This thin-walled tissue may become caducous, at least in herbarium specimens. Between the ribs the secondary xylem has numerous vessels; in the ribs the vessels are narrower and scarcer. Vessel perforations are simple. Through anomalous activity of the cambium, 5 phloem strands become enclosed within xylem in the young shoot. Later interxylary phloem is formed as continuous bands alternating with secondary xylem. The phloem is stratified into soft and fibrous portions. Axial xylem parenchyma is scarce and paratracheal (only seen in young twigs). The ground tissue of the xylem is composed of fibres with numerous minutely bordered pits. Rays vary from 1-6-seriate in the young stem. The outer phloem is surrounded by a cylinder of fibres and stone cells. Cork arises in the layer below the epidermis.
The anatomy of the leaf has hitherto never been described. The petiole shows a strongly incurved arc of separate vascular bundles and two additional latero-dorsal bundles as seen in transverse section through the distal end. The vascular system forms a closed flattened cylinder in the midrib. The stomata, confined to the abaxial surface, are paracytic. Crystals are present as solitary rhomboids and clusters. The hairs are unicellular.
To evaluate the taxonomic significance of the vegetative anatomy of Lophopyxis with regard to the affinities of the genus more research is still needed. The only straightforward conclusion to be drawn at present is that Lophopyxis is anatomically entirely different from Gouania (Rhamnaceae), to which AIRY SHAW (in Willis Dict. ed. 7, 1966, 668) related it. Gouania differs e.g. in having anomocytic stomata, styloids, unlignified perivascular fibres and exclusively narrow rays. Dr. C. R. METCALFE (Kew) kindly put slides and anatomical information of Lophopyxis and Gouania at my disposal. — P. BAAS.
Taxonomy
This genus was tentatively ascribed to the Euphorbiaceae by HOOKER f., but removed from this family by PAX (1890). ENGLER (1893) accommodated it as a distinct subfamily Lophopyxidoideae within Icacinaceae, from which I rejected it in 1942. HUTCHINSON () placed it in the Celastraceae.
Its gross morphology, wood anatomy, embryology and pollen morphology is well known and it is now apparent that it should be placed within the Geraniales-Sapindales-Celastrales. It seems, however, that it does not fit in any of the established families of these orders. Its relation to Rhamnaceae, suggested by SHAW (1966) rests on a superficial habit similarity with Gouania, as shown by ; see also sub Anatomy.
The best solution is to regard it as the type of a family of its own, as has been casually proposed by VAN TIEGHEM (1897) and PIERRE (1897), and formally by PFEIFFER (1951). I have this more fully explained in my precursory paper in .
Its gross morphology, wood anatomy, embryology and pollen morphology is well known and it is now apparent that it should be placed within the Geraniales-Sapindales-Celastrales. It seems, however, that it does not fit in any of the established families of these orders. Its relation to Rhamnaceae, suggested by SHAW (1966) rests on a superficial habit similarity with Gouania, as shown by ; see also sub Anatomy.
The best solution is to regard it as the type of a family of its own, as has been casually proposed by VAN TIEGHEM (1897) and PIERRE (1897), and formally by PFEIFFER (1951). I have this more fully explained in my precursory paper in .