The species of the tree genus Pterospermum Schreb. (Malvaceae: Dombeyoideae) in Malesia are revised. Twenty-six species of Pterospermum are recognised, six of which are new (P. aureum S.K.Ganesan, P. borneense S.K.Ganesan, P. glabrum S.K.Ganesan, P. havilandii S.K.Ganesan, P. merrillianum S.K.Ganesan and P. zollingerianum S.K.Ganesan) and one (P. grewiifolium Pierre) that is a new distributional record for Malesia. Identification keys are provided. All names are typified, and detailed descriptions of all species recognised are provided. Information on habitat, uses and conservation status is given for all species.

The host range of an isolate of the fungal pathogen Alternaria macrospora Zimmerman from infected spurred anoda [Anoda cristata (L.) Schlecht.] leaves was studied in the greenhouse and growth chamber. The fungus was inoculated to representative plants in the Malvaceae, Solanaceae, Leguminosae, and Gramineae families. Evidence of infection was limited to plants in the Malvaceae, with spurred anoda being the most susceptible species tested. Only negligible damage was incited on cotton (Gossypium hirsutum L. ‘Stoneville 213′) and long staple cotton (G. barbadense L. ‘Pima S–5′), hollyhock [Althaea rosea (L.) Cav.], okra (Hibiscus esculentus L. ‘Clemson spineless’), prickly sida (Sida spinosa L.), velvetleaf (Abutilon theophrasti Medic.), and Venice mallow (Hibiscus trionum L.). Disease symptoms induced in cotton by the spurred anoda isolate of A. macrospora were much less severe than those reported for other isolates of the fungus. Therefore, the spurred anoda isolate may be a specialized form of the fungus.

Species delimitation in Scaphium (Sterculioideae, Malvaceae/Sterculiaceae) has been problematic and has led to confusion in identification of species. The genus was last revised in 1953 and at that time comprised four species. Since then five new species have been published. This revision of Scaphium recognises eight species, with other names being accounted for in synonymy or by exclusion from the genus.

Scaphium parviflorum P.Wilkie sp. nov. (Sterculioideae, Malvaceae/Sterculiaceae) is described and illustrated. The flowers are intermediate between the tubular flowers of Scaphium macropodum and the deeply lobed ones of Scaphium affine. However, Scaphium parviflorum differs from these species by its smooth to fissured or dippled and brown to grey-brown bark, small narrowly ovate to narrowly elliptic leaves and the presence of sparse minute flattened stellate hairs (resembling scales) on the midrib of the lower surface of the lamina.

Malva parviflora L. (Malvaceae) is rapidly becoming a serious weed of Australian farming systems. An understanding of the variability of its seed behaviour is required to enable the development of integrated weed management strategies. Mature M. parviflora seeds were collected from four diverse locations in the Mediterranean-type climatic agricultural region of Western Australia. All of the seeds exhibited physical dormancy at collection; manual scarification or a period of fluctuating summer temperatures (50/20°C or natural) were required to release dormancy. When scarified and germinated soon (1 month) after collection, the majority of seeds were able to germinate over a wide range of temperatures (5–37°C) and had no light requirement. Germination was slower for seeds stored for 2 months than seeds stored for 2 years, suggesting the presence of shallow physiological dormancy. Seed populations from regions with similar annual rainfall exhibited similar dormancy release patterns; seeds from areas of low rainfall (337–344 mm) were more responsive to fluctuating temperatures, releasing physical dormancy earlier than those from areas of high rainfall (436–444 mm). After 36 months, maximum seedling emergence from soil in the field was 60%, with buried seeds producing 13–34% greater emergence than seeds on the surface. Scanning electron microscopy of the seed coat revealed structural differences in the chalazal region of permeable and impermeable seeds, suggesting the importance of this region in physical dormancy breakdown of M. parviflora seeds. The influence of rainfall during plant growth in determining dormancy release, and hence, germination and emergence timing, must be considered when developing management strategies for M. parviflora.

Aphis gossypii Glover is a polyphagous aphid pest with a worldwide distribution. However, there is evidence that on a global scale the name A. gossypii is being applied to a number of forms with different life cycles and/or host-plant associations. Morphometric variation of A. gossypii samples from crops and non-cultivated plants in many parts of the world was examined, to determine whether this variation is correlated with the hosts from which the aphids originated. Samples of A. gossypii were collected from Cucurbitaceae and Malvaceae in Europe, and from Compositae in various parts of the world. Morphometric data for 13 parameters measured from 97 clonal lineages (728 specimens) and 27 field-collected samples (313 specimens) were analysed by a series of canonical variates analyses, using the field sample/clonal lineage as grouping factor. Clonal lineages were reared on a common host in controlled conditions to standardize the effect of host and environment on morphology. The analyses provided a clear morphometric separation of the aphids originating from Compositae and those collected on Cucurbitaceae and Malvaceae, regardless of the geographical origin of the aphids and the host plant on which they were reared. This indicates that within A. gossypii there are two widely distributed host races or subspecies with different plant family associations. The taxonomic implications are discussed.