NORTHERN AND SOUTHERN HEMISPHERE HYBRIDS OF MACROCYSTIS (PHAEOPHYCEAE)1

All combinations of individuals of Macrocystis pyrifera (L.) C. Agardh, M. integrifolia Bory, and M. angustifolia Bory hybridized. Gametophyte isolates obtained from 18 individuals were used, including M. pyrifera and M. integrifolia from the extremes of their Northern Hemisphere ranges along the Pacific Coast of North America and M. pyrifera and M. angustifolia from Tasmania, Australia. All combinations of gametophytes produced sporophytes of normal morphology, with the exception of crosses involving three gametophyte isolates. One female (M. integrifolia) and two male (M. pyrifera and M. angustifolia)gametophyte isolates were unable to produce normal sporophytes in combination with gametophytes of the opposite sex. Some cultures of female gametophytes produced abnormally shaped parthenogenetic sporophytes. Gametophytes and sporangia of M. pyrifera had n= 16 chromosomes. The M. integrifolia female gametophyte that was unable to produce normal sporophytes had n = ca. 32 chromosomes. These results show that these species of Macrocystis have not become reproductively isolated. Although these species may be considered conspecific according to the biological species concept, we recommend that they continue to be recognized as separate species based on morphological differences.     

HYBRIDIZATION OF MACROCYSTIS (PHAEOPHYTA) WITH OTHER FLOAT-BEARING KELPS1,2

Sporophytes were produced in 22 out of 23 attempts to cross Macrocystia angustifolia Bory with Pelagophycus porra (Lemon) Setchell. Representative samples of these plants were raised in a surge-tank under greenhouse conditions to several meters in length. The plants resulting from this intergeneric cross were intermediate in morphology between the parental genera. The intermediate plants were similar to those found fry one of the authors (MN) in 1957, and by others since then, in California kelp beds where Macrocystis and Pelagophycus co-occur, A cross between M. angustifolia and Nereocystis luetkeana (Mertens) P. & R., also produced normal sporophytes. The taxonomic, evolutionary, morphogenetic and genetic implications of these hybridizations are discussed.     

Effects of chelated iron on oogenesis and vegetative growth of kelp gametophytes (Phaeophyceae)

The supply of iron has been reported to affect gametogenesis in the gametophytes of some species of kelps (order Laminariales). Spores of the kelps Alaria marginata Postels & Ruprecht, Dictyoneurum californicum Ruprecht, Egregia menziesii (Turner) Areschoug, Laminaria setchellii Silva, and Macrocystis pyrifera (L.) C. Agardh were cultured in enriched seawater with and without added chelated iron (Fe‐ethylenediaminetetraacetate) to determine the effects of iron on oogenesis. All species showed a decrease in oogenesis without added Fe‐ethylenediaminetetraacetic acid (EDTA). Gametophytes of E. menziesii showed predominant gametogenesis with or without supplied iron, resulting in all cells being converted to gametes so that vegetative growth did not continue. Vegetative gametophytes were obtained in the other species used. Gametophytes of M. pyrifera did not show any oogenesis without added Fe‐EDTA, while those of L. setchellii, A. marginata and D. californicum were intermediate in their response, showing some gametogenesis without added Fe‐EDTA. When Fe‐EDTA supply was delayed by 6, 13 and 20 days with spores of M. pyrifera, the gametophytes produced fewer eggs, with a greater decrease as the delay grew longer. A range of Fe‐EDTA concentrations was investigated using isolated female gametophytes of two strains of M. pyrifera and one of Macrocystis integrifolia Bory. None of these three strains produced gametes without the addition of Fe‐EDTA. Gametophytes of M. integrifolia required the least amount of added Fe‐EDTA to achieve gametogenesis while gametophytes of M. pyrifera required higher amounts, with the two strains showing somewhat different responses. Iron nutrition appears to be an essential factor for gametogenesis in several species of kelps.     

EFFECT OF HIGH IRRADIANCE ON RECRUITMENT OF THE GIANT KELP MACROCYSTIS (PHAEOPHYTA) IN SHALLOW WATER1

Laboratory and field experiments were done hi Still-water Cove, Carmel Bay, California, and Monterey Harbor, California, to determine the effect of photosynthetically active radiation (PAR) on the shallow (upper) limit of giant kelp, Macrocystis pyrifera (L.) C. Agardh. At shallow depths, M. pyrifera did not recruit or grow to macroscopic size from gametophytes or embryonic sporophytes transplanted to vertical buoy lines; sharp decreases in PAR with depth coincided with observed recruitment and sporophyte distributions. Shade manipulations indicated that settlement of M. pyrifera zoospores was decreased, but not prohibited, by high PAR. Postsettlement stages (gametophytes and embryonic sporophytes), however, survived only under shade. These results suggest that high PAR can inhibit the recruitment of M. pyrifera to shallow water by killing its postsettlement stages; whether or not ultraviolet (UV) radiation also inhibits recruitment was not tested. In either case, however, it appears that high irradiance (PAR and/or UV) regulates the shallow limit of M. pyrifera prior to temperature and desiccation stresses inherent to intertidal regions. In an additional experiment, recruitment or growth of transplanted gametophytes or embryonic sporophytes of Macrocystis integrifolia Bory also did not occur at shallow depths, suggesting that this shallow water species accesses high irradiance regions via a method other than sexual reproduction.     

EVOLUTION OF MACROCYSTIS SPP. (PHAEOPHYCEAE) AS DETERMINED BY ITS1 AND ITS2 SEQUENCES1,

Macrocystis (Lessoniaceae) displays an antitropical distribution, occurring in temperate subtidal regions along western North America in the northern hemisphere and throughout the southern hemisphere. We used the noncoding rDNA internal transcribed spacer regions (ITS1 and ITS2) to examine relatedness among (1) Macrocystis and several genera of Laminariales, (2) four species of Macrocystis ( M. integrifolia Bory from the northern hemisphere, M. angustifolia Bory and M. laevis Hay from the southern hemisphere, and M. pyrifera [L.] C. Ag. from both hemispheres), and (3) multiple clones of several individuals. Of the taxa included in our phylogenetic analysis, the elk kelp, Pelagophycus porra (Lem.) Setch., was the sister taxon to Macrocystis spp. Macrocystis individuals from the southern hemisphere (representing three species) formed a strongly to moderately supported clade, respectively, when the ITS1 and ITS2 sequences were analyzed separately. No distinction was detected between the two species in the northern hemisphere. Thus, Macrocystis may be a monospecific genus ( M. pyrifera ). A northern-hemisphere-to-southern-hemisphere pattern of dispersal was inferred, because northern-hemisphere individuals were more diverse and displayed paraphyletic clades, whereas southern-hemisphere individuals were less diverse and formed a monophyletic clade. High intraindividual variation in ITS1 sequences was observed in one individual from Santa Catalina Island (CA), suggesting very recent and rapid mixing of genotypes from areas to the north and Baja California (Mexico) or introgressive hybridization with Pelagophycus.     

DISCOVERY OF A FERTILE PELAGOPHYCUS×MACROCYSTIS(PHAEOPHYTA) PUTATIVE HYBRID AND SUBSEQUENT PRODUCTION OF F2 SPOROPHYTES IN THE LABORATORY1

A fertile putative hybrid of Pelagophycus porra (Lem.)Setch. × Macrocystis pyrifera (L.) was discovered in Big Fisherman Cove, Santa Catalina Island, California, in March 1986. The plant possessed a single, solid primary stipe that bifurcated into two secondary stipes, each with a hooked-shaped pneumatocyst. A total of 15 blades, 14 with sori, were produced on two to three dichotomies above and below each pneumatocyst. Gametophyte development of spores released from sori and the resulting early sporophtes (2–3 mm) were typical of Laminariales. Gametophytes appeared within a day of spore germination, 500-cell stage sporophytts within 3–4 weeks, and 2–3 mm sporophytes within 5–6 weeks. The cultures expired before branching patterns could be determined.     

AN EVALUATION OF METHODS USED TO ASSESS INTERGENERIC HYBRIDIZATION IN KELP USING PACIFIC LAMINARIALES (PHAEOPHYCEAE)1

Kelp intergeneric laminarialean hybridizations and hybridization protocol were assessed using seven northeast Pacific kelp species: Alaria marginata Postels and Ruprecht, Costaria costata (C. A. Agardh) Saunders, Eisenia arborea Areschoug, Laminaria saccharina (L) Lamouroux, Lessoniopsis littoralis (Tilden) Reinke, Macrocystis integrifolia Bory, and Nereocystis leutkeana (Mertens) Postels and Ruprecht. Survival and development of sporophyte morphologies derived from selfings, separate males and females, and reciprocal crosses were evaluated over 30 weeks of cultivation. All cultures were initiated from cloned gametophytes. Two closely related species, Laminaria angustata Kjellman and L. japonica Areschoug, demonstrated the efficacy of long‐term (up to 30 years) cloned gametophytes in hybridization studies. Sporophyte morphologies appeared in 34%–69% of control and hybridization trials, and 6%–16% of all trials produced sporophytes in control and hybridization conditions that persisted through 30 weeks of cultivation. Sporophytes in control and hybridization conditions could appear normal or abnormal. Usually, the morphology of sporophytes in hybridizations and female controls resembled the female parent, whereas the sporophytes in male controls often had an abbreviated morphology, lacking definitive generic features. Species‐specific rDNA internal transcribed spacer molecular primers were used to determine the parentage of five putative hybrids. Only the L. japonica♀/L. angustata♂ hybrid bore both parental genomes. That negative controls could produce persistent and normal‐appearing sporophytes negates their value and emphasizes the importance of molecular confirmation in hybridization studies. These findings were applied to critique the only known wild intergeneric hybrid, Pelagophycus/Macrocystis.     

100 Effects of chelated iron on gametogenesis in kelp gametophytes

Gametogenesis in several species of kelp gametophytes was investigated in relation to the supply of chelated iron (Fe-EDTA) in the culture medium. Spores of Laminaria setchellii, Egregia menziesii, Alaria marginata, Dictyoneurum californicum , and Macrocystis pyrifera were grown in Provasoli's Enriched Seawater with and without added Fe-EDTA. All species showed a decrease in gametogenesis without added Fe-EDTA. Gametophytes of E. menziesii showed predominant gametogenesis even without supplied iron, resulting in all cells being converted to gametes so that vegetative growth did not continue. Vegetative gametophytes were obtained in the other species. M. pyrifera did not show any gametogenesis without added Fe-EDTA. L. setchellii, A. marginata and D. californicum were intermediate in their response. In addition, Fe-EDTA supply was delayed by 1, 2 and 3 weeks with spores of M. pyrifera , resulting in an intermediate degree of gametogenesis which decreased as the delay grew longer. Fe-EDTA supply was also investigated using isolated female gametophytes of two strains of M. pyrifera and one of Macrocystis integrifolia . None of the three strains produced gametes without the addition of Fe-EDTA. Gametophytes of M. integrifolia required the least amount of added Fe-EDTA to achieve gametogenesis while gametophytes of M. pyrifera required higher amounts, with the two strains showing different responses. Thus, by varying the supply of chelated iron, it is possible to control vegetative growth or gametogenesis in most of these kelp species. In addition, different species and individuals show varied responses to added chelated iron.     

A MULTISPECIES LABORATORY ASSESSMENT OF RAPID SPOROPHYTE RECRUITMENT FROM DELAYED KELP GAMETOPHYTES1

Recent work suggests that the ability to delay reproduction as resistant haploid gametophytes may be important for seaweeds that experience unpredictable disturbances or seasonal periods of poor conditions that result in adult sporophyte absence. Further, delayed gametophytes of some kelp species (order Laminariales) may produce sporophytes more rapidly than if they had never experienced a delay, conferring a competitive advantage when conditions improve or after disturbance events. Here, it was determined that the gametophytes of the canopy‐forming kelp Macrocystis pyrifera (L.) C. Agardh could delay reproduction in a one‐ to two‐cell state (<50 μm) for at least 7 months when grown under nutrient‐limiting conditions. These stages retained reproductive viability and produced sporophytes within 5 d once nutrients were increased. This finding suggests that gametophytes could potentially promote recovery of M. pyrifera populations after extended periods of sporophyte absence. In addition, the time required for sporophyte production between gametophytes of the four most conspicuous kelp species in Southern California that had delayed reproduction and gametophytes that had not was compared. For these four kelp species, a delay of at least 30 d conferred a 40%–76% reduction in the time required for sporophyte production once nutrients were received. Fecundity did not decrease with delay duration, suggesting there is no apparent cost of delayed development for kelps as has been observed in other organisms. Thus, delayed development may be a viable strategy for surviving and initially dominating in environments with variable quality.     

CHELATED IRON AND GAMETOGENESIS IN MACROCYSTIS

Stekoll, M. S. Juneau Center for Fisheries and Ocean Sciences, University of Alaska, Juneau, AK 99801 USA Gametophytes of Macrocystis can be vegetatively propagated indefinitely in the laboratory in media that lacked chelated iron. When clones of vegetatively propagated female gametophytes of Macrocystis pyrifera (L.) C. Ag. were exposed to varying levels of chelated iron in both enriched natural and artificial seawater, low levels of chelated iron (1-5 micromoles/liter) stimulated the onset of gametogenesis as measured by egg production. In contrast higher iron concentrations strongly inhibited egg production. Gametophyte growth as measured by the increase in cell number was not affected by iron concentration in the medium. At all iron concentrations there was a tendency for the larger gametophytic fragments to become fertile earlier. The results suggest that iron may play a critical role in the development of Macrocystis gametophytes.     

EFFECTS OF LIGHT AND TEMPERATURE ON NET PHOTOSYNTHESIS AND DARK RESPIRATION OF GAMETOPHYTES AND EMBRYONIC SPOROPHYTES OF MACROCYSTIS PYRIFERA1

The rates of net photosynthesis as a function of irradiance and temperature were determined for gametophytes and embryonic sporophytes of the kelp, Macrocystis pyrifera (L.) C. Ag. Gametophytes exhibited higher net photosynthetic rates based on oxygen and pH measurements than their derived embryonic sporophytes, but reached light saturation at comparable irradiance levels. The net photosynthesis of gametophytes reached a maximum of 66.4 mg O₂ g dry wt^?1 h^?1 (86.5 mg CO₂ g dry wt^?1 h^?1), a value approximately seven times the rate reported previously for the adult sporophyte blades. Gametophytes were light saturated at 70 μE m^?2 s^?1 and exhibited a significant decline in photosynthetic performance at irradiances 140 μE m^?1 s^?1. Embryonic sporophytes revealed a maximum photosynthetic capacity of 20.6 mg O₂ g dry wt^?1 h^?1 (25.3 mg CO₂ g dry wt^?1 h^?1), a rate about twice that reported for adult sporophyte blades. Embryonic sporophytes also became light saturated at 70 μE m^?2 s^?1, but unlike their parental gametophytes, failed to exhibit lesser photosynthetic rates at the highest irradiance levels studied; light compensation occurred at 2.8 μE m^?2 s^?1. Light-saturated net photosynthetic rates of gametophytes and embryonic sporophytes varied significantly with temperature. Gametophytes exhibited maximal photosynthesis at 15° to 20° C, whereas embryonic sporophytes maintained comparable rates between 10° and 20° C. Both gametophytes and embryonic sporophytes declined in photosynthetic capacity at 30° C. Dark respiration of gametophytes was uniform from 10° to 25° C, but increased six-fold at 30° C; the rates for embryonic sporophytes were comparable over the entire range of temperatures examined. The broader light and temperature tolerances of the embryonic sporophytes suggest that this stage in the life history of M. pyrifera is well suited for the subtidal benthic environment and for the conditions in the upper levels of the water column.     

Chromosomal inheritance patterns of intergeneric hybrids of ictalurid catfishes: odd diploid numbers with equal parental contributions

Hybrid chromosomal compositions of channel catfish Ictalurus punctatus × black bullhead Ameiurus melas and channel catfish × flathead catfish Pylodictis olivaris were analysed by a computer-based method. The karyotype of each hybrid was highly asymmetric, and the diploid numbers and arm numbers were intermediate to the parental types. The hybrid offspring of channel catfish × black bullhead possessed a diploid number of 59 chromosomes, with an arm number estimate of 87. The hybrid offspring of the channel catfish × flathead catfish cross possessed a diploid number of 57 chromosomes, also with an arm number estimate of 87. Nucleolus organizer regions (NORs) were located on a single pair of chromosomes with symmetric staining intensity in channel catfish and in black bullhead, and on a single pair of chromosomes with asymmetric staining intensity in flathead catfish. The channel catfish × black bullhead hybrid had two unpaired chromosomes that stained positively for NORs. The channel catfish × flathead catfish had three unpaired chromosomes that stained positively for NORs. Specific marker chromosomes were identified in each hybrid. There was no evidence of androgenesis, gynogenesis, polyploidy or aneuploidy in the hybrids. Results of this study, plus information reported previously, indicate that chromosomes of ictalurid catfishes are inherited stably in a haploid pattern with an equal contribution to the genomes of F₁ hybrids, even in intergeneric crosses involving divergent numbers of parental chromosomes.     

Nuclear DNA level and life cycle of kelps: Evidence for sex‐specific polyteny in Macrocystis (Laminariales,Phaeophyceae)

Giant kelp, Macrocystis pyrifera (Linnaeus) C. Agardh, is the subject of intense breeding studies for marine biomass production and conservation of natural resources. In this context, six gametophyte pairs and a sporophyte offspring of Macrocystis from South America were analyzed by flow cytometry. Minimum relative DNA content per cell (1C) was found in five males. Unexpectedly, nuclei of all female gametophytes contained approximately double the DNA content (2C) of males; the male gametophyte from one locality also contained 2C, likely a spontaneous natural diploid variant. The results illustrate a sex‐specific difference in nuclear DNA content among Macrocystis gametophytes, with the chromosomes of the females in a polytenic condition. This correlates with significantly larger cell sizes in female gametophytes compared to males and resource allocation in oogamous reproduction. The results provide key information for the interpretation of DNA measurements in kelp life cycle stages and prompt further research on the regulation of the cell cycle, metabolic activity, sex determination, and sporophyte development.     

37 Production, survival and morphology of kelp (protista) "sporophytes" arising from selfings, apogamy and hybridizations

The production and survival of sporophyte morphologies that arose from selfings, parthenogenesis, male apogamy and reciprocal hybridizations of Costaria costata (C.A. Agardh) Saunders, Laminaria saccharina (L) Lamouroux, Alaria marginata Postels and Ruprecht, Eisenia arborea Areschoug, Lessoniopsis littoralis (Tilden) Reinke, Macrocystis integrifolia Bory, and Nereocystis leutkeana (Mertens) Postels and Ruprecht was tracked for 215 hybridization trials for 30 weeks. Each trial consisted of selfings for each species, solo cultures of males and females for each species and reciprocal crossings. At the end of 30 weeks, "sporophyte" survival in the 215 cases was 13% for selfings, 10% for parthenogenesis, 6% for apogamy, and 16% for the reciprocal hybridizations. The morphologies of sporophytes resulting from selfings were typical of the selfed species. Parthenosporophytes and reciprocal hybrids usually had the distinctive morphology of the female parent. Male, apogamously derived "sporophytes" often had reduced morphological features. For example, A. marginata male apogamous sporophytes often lacked a midrib. The sporophyte morphologies that arose in the reciprocal crossings are considered to be putative hybrids. Molecular evidence is required to establish their genetic origins.     

ETIOLOGY AND DEVELOPMENT OF HYPERPLASIA INDUCED BY STREBLONEMA SP. (PHAEOPHYTA) ON MEMBERS OF THE LAMINARIALES (PHAEOPHYTA)1

Filaments of Streblonema sp. isolated from hyperplasia (galls) on Nereocystis luetkeana (Mert.) Post. et Rupr. induced similar gall growths when inoculated on young sporophytes of Nereocystis luetkeana, Macrocystis integrifolia Bory, and Laminaria japonica Aresch. Filaments were irregularly branched and uniseriate with cells 5–8 μm in diameter and 10–30 μm long. Growth under varied cultured conditions produced unilocular sporangia. Zoospores released from the sporangia germinated into identical filaments which also formed unilocular sporangia. Gall tissue originated from the innermost cells of the epidermal meristematic zone. When infected these cells divided in an irregular and unorganized manner. The resulting structure was a pronounced departure from normal morphology.     

THE EFFECTS OF HIGH IRRADIANCE ON THE SETTLEMENT COMPETENCY AND VIABILITY OF KELP ZOOSPORES1

Elevated irradiance has a profound effect on the successful dispersal and establishment of kelp zoospores, affecting their physiology and viability. The research to date, however, has been on zoospores localized near the benthos, with little attention on the importance of vertical transportation and subsequent exposure to increased irradiance. Therefore, we wanted to investigate the effects of exposure to high irradiance on the reproductive planktonic life‐history stages of kelps Macrocystis pyrifera (L.) C. Agardh and Pterygophora californica Rupr. Zoospores of both species were exposed to different irradiances (75, 275, 575, 1,025 μmol photons · m^?2 · s^?1) over varying durations (1, 2, 4, 8, 12 h) and subsequently monitored for settlement competency, gametophyte development, and reproductive viability. Settlement success for M. pyrifera was uniform throughout all irradiance × time treatments, while settlement for P. californica decreased with increasing exposure time but not irradiance, although settlement was generally reduced at the highest irradiance level. Following zoospore settlement, germ tube development was visible in the gametophytes of both species within 1 week, although a significant decline of germ tube density in P. californica was observed with increasing irradiance. Similarly, a decrease in germ tube development with increasing exposure was observed across all irradiance levels for M. pyrifera, but irradiance itself was not significant. Further development into embryonic sporophytes was remarkably similar to gametophyte development, suggesting that the effect of exposure of kelp zoospores to high irradiance on subsequent sporophyte production is mediated through gametophyte development as well as zoospore survival.     

A LOW-VOLUME FLOW TANK FOR MEASURING NUTRIENT UPTAKE BY LARGE MACROPHYTES1

A recirculating flow-tank was designed and tested to measure inorganic nutrient uptake by, and visualize the movement of seawater around, large macrophytes. The tank volume was small (46 L), and a propeller drive produced unidirectional mean flow. A turbulence reduction section dampened turbulence in the test section to a low level, so that water movement within this region was virtually laminar. The test section of the tank was wider than that of previous designs, allowing whole blades of Macrocystis integrifolia Bory and juvenile plants of Nereocystis luetkeana (Mert.) Post, et Rupr. to be placed in the flow, away from the influence of velocity boundary layers associated with the tank walls. The tank's use in macroalgae nutrient uptake and flow visualization experiments was demonstrated.     

Preferential accumulation of d-pinitol in Acrostichum aureum gametophytes in response to salt stress

Growth and metabolic responses to salt stress were studied in gametophytes of Acrostichum aureum L. (a mangrove fern). Gametophytes were cultured in 0–170 m M NaCl solutions. The growth of gametophytes was best in low NaCl concentrations (35 and 85 m M ), and was retarded at higher NaCl concentrations. Photosynthetic rate of gametophytes was also significantly reduced when grown in high NaCl concentrations. Severe salt stress (>120 m M NaCl) led to a preferential accumulation of d -pinitol in gametophytes, whereas the sporophyte accumulated d -1- O -methyl- muco -inositol. The content of d -pinitol reached up to 50% of the soluble carbohydrate pool of gametophytes under 155 and 170 m M NaCl. The accumulation of d -pinitol and other cyclitols in gametophytes was correlated with the retention of photochemical efficiency of photosystem II and the survival of gametophytes after transfer to solutions containing 340 and 600 m M NaCl, respectively.     

Gametogenesis and chromosome number in Postelsia palmaeformis (Laminariales, Phaeophyceae)

Gametophytes of the ‘sea palm’, the kelp Postelsia palmaeformis Ruprecht, produced gametes whether or not chelated iron was supplied in the culture medium, in contrast to the inhibition of gametogenesis seen with the absence of iron in many other kelps. As gametogenesis proceeded, every cell of the gametophytes was converted into a gamete so that the gametophytes did not continue to grow vegetatively. The portion of the life history from spore release through germination, gametophyte growth, gametogenesis, fertilization and growth of the young sporophyte was completed in 9–10 days under laboratory conditions. Chromosome counts showed that sporophytes had a diploid number of 26–34 chromosomes while sporangia and gametophytes had a haploid number of 14–17 chromosomes, indicating a typical haplodiplophasic life history as seen in other Laminariales.     

INTERGENERIC HYBRIDIZATION,INDUCED POLYPLOIDY,AND THE ORIGIN OF THE HAWAIIAN ENDEMIC LIPOCHAETA FROM WEDELIA (COMPOSITAE)

The genetic relationships of the Hawaiian endemic genus Lipochaeta and the nearly cosmopolitan but extra-Hawaiian genus Wedelia were assessed by way of experimental hybridization. Hybrids between Wedelia biflora and diploid species of Lipochaeta consistently exhibited 15 pairs of chromosomes at meiosis, whereas the modal and maximum configuration seen in hybrids between W. biflora and tetraploid species of Lipochaeta was 15_II + 11_I. Meiotic pairing in microsporocytes of the intergeneric hybrid combinations involving Wedelia trilobata and both sections of Lipochaeta is lower than in intergeneric hybrids involving W. biflora. All of the intergeneric F, hybrids produced had relatively low pollen stainabilities ranging from less than 1–16% and, although they were vegetatively vigorous, they failed to produce viable achenes. The effects of chromosome doubling by colchicine in one species and several hybrids in Lipochaeta and in one intergeneric hybrid between Lipochaeta and Wedelia were studied. Chromosome doubling of the diploid species caused a decrease in pollen stainability and resulted in lack of achene production, whereas doubling the chromosomes of sterile intersectional and intergeneric hybrids restored female fertility and effected a dramatic increase in pollen stainability. Cytological analysis of the microsporocytes at diakinesis and metaphase I revealed pairs and quadrivalents in the induced polyploids. Pollen measurements indicated that pollen size in Lipochaeta is correlated with doubling of the chromosomes. Statistical analyses revealed that there is no significant difference in pollen size between the diploids and natural tetraploids, whereas both groups have pollen grains that are significantly smaller than the induced autotetraploid, the intergeneric allotetraploid, and the intersectional allohexaploid. The cytogenetic evidence indicates a relatively close genetic relationship between Wedelia and Lipochaeta and supports the view that the ancestry of the diploid section Aphanopappus of Lipochaeta (n = 15) is to be found in a species akin to Wedelia biflora (n = 15) and that this or a similar 15-paired wedelioid species and an unknown 11-paired wedelioid taxon are involved in the alloploid hybrid origin of the tetraploid section Lipochaeta (n = 26) of Lipochaeta.