Determinate Inflorescences Research Articles

BnaC09.tfl1 controls determinate inflorescence trait in Brassica napus

Determinate inflorescence is indeed a pivotal agricultural characteristic in crops, notably impacting the architecture modification of Brassica napus (AACC, 2n = 38). Previous study identified a crucial gene Bnsdt2 that encodes the transcription factor BnaC09.TFL1 (Terminal Flower 1). Here by two alleles were cloned and sequenced from indeterminate 2982 and determinate 4769, respectively, we found that BnaC09.TFL1 harbors two T/C and G/C non-synonymous mutations in exon 1, and contains sixty-six differences in a 1.9 Kb promoter sequence. Subsequently, BnaC09.TFL1 was introduced into B. napus 571 line by genetic complementation and overexpression, transgenic plants 571CTO lines and 571TClines were all restored to the indeterminate inflorescence. Interestingly, after BnaC09.TFL1 was knocked out in ‘Westar’, transgenic plants WestarTcr lines were mutated to determinate inflorescences. Additionally, a NIL-4769 line was constructed to evaluate the effect of BnaC09.TFL1 on agronomic traits of Brassica napus, the results demonstrated that BnaC09.tfl1 reduced the plant height and increased the branch number and branch thousand grain weight of Brassica napus. Finally, we performed RT-qPCR, GUS staining and subcellular localization experiments to analyze the expression pattern of BnaC09.TFL1, the results showed that the expression of BnaC09.TFL1 at shoot apex of NIL-4769 was higher than that of 4769, GUS activity was detected at apical of Arabidopsis thaliana and BnC09.TFL1-GFP was detected in cell membrane, nucleus and cytoplasm. Our findings provide a firm molecular foundation for the study of rapeseed’s molecular mechanism of determinate inflorescence formation, as well as theoretical guidance for the application of determinate inflorescence in rapeseed breeding.

Exploration into Natural Variation Genes Associated with Determinate and Capitulum-like Inflorescence in Brassica napus.

Brassica napus is a globally important vegetable and oil crop. The research is meaningful for the yield and plant architecture of B. napus. In this study, one natural mutant line with determinate and capitulum-like inflorescence was chosen for further study. Genetic analysis indicated that the segregation patterns of inflorescences in the F2 populations supported a digenic inheritance model, which was further approved via the BSA-Seq technique. The BSA-Seq method detected two QTL regions on C02 (14.27-18.41 Mb) and C06 (32.98-33.68 Mb) for the genetic control of determinate inflorescences in MT plants. In addition, the expression profile in MT compared with WT was analyzed, and a total of 133 candidate genes for regulating the flower development (75 genes, 56.4%), shoot meristem development (29 genes, 21.8%), and inflorescence meristem development (13 genes, 9.8%) were identified. Then one joint analysis combing BSA-Seq and RNA-Seq identified two candidate genes of BnaTFL1 and BnaAP1 for regulating the MT phenotype. Furthermore, the potential utilization of the MT plants was also discussed.

Advances in Citrus Flowering: A Review.

Citrus are polycarpic and evergreen species that flower once in spring or several times a year depending on the genotype and the climatic conditions. Floral induction is triggered by low temperature and water-deficit stress and occurs 2–3 months before bud sprouting, whereas differentiation takes place at the same time as sprouting. The induced buds develop single flowers or determinate inflorescences, so that vegetative growth is required at the axillary buds to renew the polycarpic habit. The presence of fruits inhibits sprouting and flower induction from nearby axillary buds in the current season. In some species and cultivars, this results in low flowering intensity the following spring, thus giving rise to alternate bearing. A number of key flowering genes act in the leaf (CiFT3, CcMADS19, etc.) or in the bud (CsLFY, CsTFL1, etc.) to promote or inhibit both flowering time and reproductive meristem identity in response to these climatic factors, the fruit dominance, or the age of the plant (juvenility). The expression of some of these genes can be modified by gibberellin treatments, which reduce bud sprouting and flowering in adult trees, and constitute the main horticultural technique to control flowering in citrus. This review presents a comprehensive view of all aspects of the flowering process in citrus, converging the research published during the past half century, which focused on plant growth regulators and the nutritional source-sink relationships and guided research toward the study of gene transcription and plant transformation, and the advances made with the development of the tools of molecular biology published during the current century.

Hormonal and carbohydrate control of fruit set in avocado ‘Lamb Hass’. A question of the type of inflorescence?

The avocado tree (Persea americana Mill.) has two types of shoots, indeterminate, which maintain vegetative development from an apical bud, and determinate, which do not have vegetative growth. Indeterminate shoots set fewer fruits than determinate ones, and significantly hasten physiological fruitlet abscission. The competition between vegetative and flower development is accepted as the most reasonable hypothesis to explain the differences. However, our results show that from anthesis until fruit set flowers of indeterminate inflorescences, both those remaining on the tree and those abscised, had a higher sucrose and C6 carbohydrate content than flowers of determinate ones and no differences between them were found for C7 carbohydrates, which disagrees with this hypothesis, and indicates that factors other than carbohydrate content are responsible for fruit set in avocado.At anthesis and fruit set stage, gibberellin and cytokinin concentrations (mainly GA1 and tZ, respectively) were significantly higher in flowers of determinate inflorescences than in those of indeterminate ones, indicating their higher ability to set.We conclude that fruit set is hormonally regulated in avocado, irrespective of vegetative growth. The lower fruit set of the indeterminate inflorescences does not depend on the competition for photosynthates due to the apical vegetative growth, since C6 and C7 carbohydrate availability is enough to ensure fruit set, but on their lower content of GA1 and tZ.

INTERMEDIUM-M encodes an HvAP2L-H5 ortholog and is required for inflorescence indeterminacy and spikelet determinacy in barley

Inflorescence architecture dictates the number of flowers and, ultimately, seeds. The architectural discrepancies between two related cereals, barley and wheat, are controlled by differences in determinacy of inflorescence and spikelet meristems. Here, we characterize two allelic series of mutations named intermedium-m (int-m) and double seed1 (dub1) that convert barley indeterminate inflorescences into wheat-like determinate inflorescences bearing a multifloreted terminal spikelet and spikelets with additional florets. INT-M/DUB1 encodes an APETALA2-like transcription factor (HvAP2L-H5) that suppresses ectopic and precocious spikelet initiation signals and maintains meristem activity. HvAP2L-H5 inhibits the identity shift of an inflorescence meristem (IM) to a terminal spikelet meristem (TSM) in barley. Null mutations in AP2L-5 lead to fewer spikelets per inflorescence but extra florets per spikelet. In wheat, prolonged and elevated AP2L-A5 activity in rAP2L-A5 mutants delays but does not suppress the IM-TSM transition. We hypothesize that the regulation of AP2L-5 orthologs and downstream genes contributes to the different inflorescence determinacy in barley and wheat. We show that AP2L-5 proteins are evolutionarily conserved in grasses, promote IM activity, and restrict floret number per spikelet. This study provides insights into the regulation of spikelet and floret number, and hence grain yield in barley and wheat.

Inflorescence Meristem Fate Is Dependent on Seed Development and FRUITFULL in Arabidopsis thaliana.

After a vegetative phase, plants initiate the floral transition in response to both environmental and endogenous cues to optimize reproductive success. During this process, the vegetative shoot apical meristem (SAM), which was producing leaves and branches, becomes an inflorescence SAM and starts producing flowers. Inflorescences can be classified in two main categories, depending on the fate of the inflorescence meristem: determinate or indeterminate. In determinate inflorescences, the SAM differentiates directly, or after the production of a certain number of flowers, into a flower, while in indeterminate inflorescences the SAM remains indeterminate and produces continuously new flowers. Even though indeterminate inflorescences have an undifferentiated SAM, the number of flowers produced by a plant is not indefinite and is characteristic of each species, indicating that it is under genetic control. In Arabidopsis thaliana and other species with indeterminate inflorescences, the end of flower production occurs by a regulated proliferative arrest of inflorescence meristems on all reproductive branches that is reminiscent of a state of induced dormancy and does not involve the determination of the SAM. This process is controlled genetically by the FRUITFULL-APETALA2 (FUL-AP2) pathway and by a correlative control exerted by the seeds through a mechanism not well understood yet. In the absence of seeds, meristem proliferative arrest does not occur, and the SAM remains actively producing flowers until it becomes determinate, differentiating into a terminal floral structure. Here we show that the indeterminate growth habit of Arabidopsis inflorescences is a facultative condition imposed by the meristematic arrest directed by FUL and the correlative signal of seeds. The terminal differentiation of the SAM when seed production is absent correlates with the induction of AGAMOUS expression in the SAM. Moreover, terminal flower formation is strictly dependent on the activity of FUL, as it was never observed in ful mutants, regardless of the fertility of the plant or the presence/absence of the AG repression exerted by APETALA2 related factors.

Characterization of the BnA10.tfl1 Gene Controls Determinate Inflorescence Trait in Brassica napus L.

Determinate inflorescences have a significant effect on the genetic improvement of rapeseed, so understanding the molecular function underlying the inflorescence trait may be beneficial to oilseed breeding. A previous study found candidate gene BnTFL1 (Terminal Flower 1) for control of the inflorescence trait on Brassica napus chromosome A10 (16,627–16,847 kb). However, little is known about the function of the BnTFL1 gene in B. napus. In this study, we firstly studied the formation of the shoot apical meristem and gene expression in indeterminate and determinate inflorescences; the results showed that the inflorescence architecture and BnA10.TFL1 expression showed significant differences in the shoot apex at the budding stage. Then, two alleles (named BnA10.TFL1 gene from indeterminate and BnA10.tfl1 gene from determinate) were cloned and sequence-analyzed; the results suggest that the open reading frame of the alleles comprises 537 bp, encodes 178 amino acids containing a conserved phosphatidylethanolamine-binding protein (PEBP) domain, and shares high similarity with Arabidopsis thaliana TFL1. To analyze the function of BnA10.TFL1, the BnA10.TFL1 gene was introduced into the determinate A. thaliana tfl1 mutant and B. napus 571 line by complementation experiment. The determinate traits were restored to indeterminate, and expression of BnA10.TFL1 was increased in the indeterminate shoot apex. These results reveal that BnA10.tfl1 is a gene controlling the determinate inflorescence trait. Moreover, the BnA10.TFL1 protein was localized to the nucleus, cytoplasm, and plasma membrane. Collectively, the results of this study help us to understand the molecular mechanism of determinate inflorescences and will provide a reliable research basis for the application of determinate inflorescences in B. napus.

Unusual positional effects on flower sex in an andromonoecious tree: Resource competition, architectural constraints, or inhibition by the apical flower?

Two, nonmutually exclusive, mechanisms-competition for resources and architectural constraints-have been proposed to explain the proximal to distal decline in flower size, mass, and/or femaleness in indeterminate, elongate inflorescences. Whether these mechanisms also explain unusual positional effects such as distal to proximal declines of floral performance in determinate inflorescences, is understudied. We tested the relative influence of these mechanisms in the andromonoecious wild olive tree, where hermaphroditic flowers occur mainly on apical and the most proximal positions in determinate inflorescences. We experimentally increased the availability of resources for the inflorescences by removing half of the inflorescences per twig or reduced resource availability by removing leaves. We also removed the apical flower to test its inhibitory effect on subapical flowers. The apical flower had the highest probability of being hermaphroditic. Further down, however, the probability of finding a hermaphroditic flower decreased from the base to the tip of the inflorescences. An experimental increase of resources increased the probability of finding hermaphroditic flowers at each position, and vice versa. Removal of the apical flower increased the probability of producing hermaphroditic flowers in proximal positions but not in subapical positions. These results indicate an interaction between resource competition and architectural constraints in influencing the arrangement of the hermaphroditic and male flowers within the inflorescences of the wild olive tree. Subapical flowers did not seem to be hormonally suppressed by apical flowers. The study of these unusual positional effects is needed for a general understanding about the functional implications of inflorescence architecture.

Optimization of controlled pollination in avocado (Persea americana Mill., Lauraceae)

Avocado has a singular synchronous protogynous dichogamy breeding system that promotes outcrossing. In this work different steps have been optimized to improve controlled pollinations in avocado in order to perform basic studies of reproductive biology and directed crosses in breeding programs. The results show that, in order to achieve successful fruit set, male flowers should be collected when all the anthers have dehisced and the pollen transferred by direct contact of the anthers with the stigma during the female stage using preferentially determinate inflorescences and pollinating at least 11 flowers per inflorescence. To perform crosses between cultivars of complementary floral groups, the flowers should be stored under high relative humidity during the hand pollination process. When the crosses involved cultivars of the same floral group, the male flowers should be collected just before anther dehiscence and could be stored for several days at 4°C. Pollen application should be performed preferentially on flowers within determinate inflorescences or within indeterminate inflorescences where vegetative growth has been removed. The results obtained are useful to optimize controlled pollinations in avocado and can help to increase fruit set in breeding programs and avoid the incorrect interpretation from pollination experiments in studies of reproductive biology.

A new combination in Peristethium (Loranthaceae) expands the genus' range into the Amazon-Cerrado ecotone

The genus Peristethium, characterized by determinate inflorescences protected by deciduous bracts, occurs in the northwest of South America, as well as Costa Rica and Panama. The main objective of this paper was to transfer one species to what we believe is its correct generic placement in Peristethium, that likewise implies in a shift of the genus' distribution beyond the Amazon. A new combination, Peristethium reticulatum, is proposed, based on Struthanthus reticulatus, described from Tocantins in 1980. The sexual dimorphism of the inflorescences of P. reticulatum (sessile male flowers and pedicellate female flowers) associated with male inflorescences that are inserted at leafless nodes are unique within the genus. The male flowers have dimorphic stamens, well-developed anthers and a pistiloid, whilst female flowers have robust styles and stigmas, and much reduced staminodes. Peristethium reticulatum and P. polystachyum occurs in the Amazon regions of Brazil, with the former recorded also in the ecotone with the Central Brazilian savannas (Cerrados).

Reinstatement and Expansion of the GenusPeristethium(Loranthaceae)1

The genus Peristethium Tiegh. (Loranthaceae) is re-established to comprise five species previously placed in Struthanthus Mart. (P. aequatoris (Kuijt) Kuijt, P. leptostachyum (Kunth) Tiegh., P. lojae (Kuijt) Kuijt, P. polystachyum (Ruiz & Pav.) Kuijt, and the new nomenclatural combination presented here, P. tortistylum (Kuijt) Kuijt). Also included are five species from Cladocolea Tiegh. (P. archeri (A. C. Sm.) Kuijt, P. peruviense (Kuijt) Kuijt, and P. primarium (Kuijt) Kuijt), with two transferred as new nomenclatural combinations herein, P. nitidum (Kuijt) Kuijt and P. roraimense (Steyerm.) Kuijt). Additionally, five new species are described and illustrated (P. attenuatum Kuijt, P. colombianum Kuijt, P. confertiflorum Kuijt, P. lamprophyllum Kuijt, and P. palandense Kuijt). The genus Peristethium thus consists of 15 species and a key is provided for the genus. It is characterized by pairs of conspicuous, often caducous, chaffy scale leaves at the base of the mostly determinate inflorescences, and by lateral inflorescence units that are triads and/or ebracteolate single flowers called monads (in one case, partly pentads). Some species have bisexual flowers while others are dioecious; flowers are either tetramerous or hexamerous, and one pentamerous species is included (P. nitidum). The minute anthers are sessile or nearly so, placed far above the middle of the petals. Geographically, the genus reaches from northern Bolivia to Costa Rica, with two rare, narrow endemics on Mt. Roraima in Venezuela and the Pakaraima Mountains.

The role of fungal pathogens in flower size and seed mass variation in three species of Hydrophyllum (Hydrophyllaceae)

Identifying ecological factors that affect seed number and seed size is key to understanding the persistence of large seed mass variation in some plant species. Pathogens may increase seed mass variation by increasing resource demand over the growing season such that late fruits experience higher resource competition than early fruits. We tested whether Fusarium sp. and Rhizoctonia sp., soil fungi that cause wilt, contributed to seasonal decline in flower size, seed number, or seed mass in Hydrophyllum appendiculatum and H. canadense. A third species not infected by these soil fungi, H. virginianum, was studied to determine how seasonal decline in floral traits and seed mass variation varies within this genus. Flower size declined seasonally for all species, but was greatest for H. appendiculatum, a monocarpic biennial with indeterminate inflorescences. Seed number decreased between first and last inflorescences in H. appendiculatum, but not in H. canadense or H. virginianum, perennials with determinate inflorescences. Seed mass varied most in H. appendiculatum and H. canadense (4-20-fold in 50% of individuals) and least in H. virginianum (4-8-fold in >30% of individuals). Fungal infection increased seed mass variation among diseased plants in H. canadense and H. appendiculatum. However, within plants fungal infection only increased seasonal decline in flower size, seed number, and seed mass in H. appendiculatum when flowers received supplemental pollination.

SOLUBLE SUGAR CONTENT IN LEAVES AND INFLORESCENCES OF THREE CULTIVARS OF AVOCADO (Persea Americana MilI.)

Total and reducing sugar content was quantified in determinate inflorescences (autumn) of ‘Colin V-33’ avocado, in leaves, and in indeterminate inflorescences (winter) of ‘Colin V’33,’ ‘Hass,’ and ‘Fuerte,’ in order to determine whether sugar content is different among inflorescences, parts of the inflorescences and cultivars. The research was carried out in Coatepec Harinas, Mexico. The to-tal sugar content was highest in ‘Colin V-33’ autumn leaves and inflorescences. The total sugar content was higher in the shoot of ‘Colin V-33’ indeterminate inflorescence. ‘Colin V-33’ determinate inflorescences had more total sugar content in their basal part (50.7 mg.g-1 f.w.), while the shoot of indeterminate inflorescences had the highest content (64.5 mg.g-1 f.w.). Comparing the three cultivars, it can be observed that ‘Fuerte’ had more reducing sugars in leaves and shoots (29.9 and 15.8 mg.g-1 f.w., respectively).

Winter trunk injections of gibberellic acid altered the fate of `Hass' avocado buds: Effects on inflorescence type, number and rate of development

SummaryThe objective of this study was to quantify the effects of high GA3 concentrations applied through trunk injection on the developmental fate of buds of young (glasshouse study) and mature (field study) `Hass' avocado (Persea americana Mill.) trees. The goal of this research was to determine whether a high dose of GA3 could be used to promote vegetative growth, reduce flowering intensity and fruit set and to even out alternate bearing. In both studies, GA3 injections were made at bud swell, prior to bud break. For young trees, injections of 25 or 50 mg GA3 per tree caused precocious inflorescence development and anthesis three weeks earlier than in control trees. GA3 injections did not affect the number of vegetative shoots produced but increased the number of indeterminate inflorescences, at the expense of determinate ones. Increased bud abscission resulting from the GA3 treatments reduced total inflorescence number. Mature trees in a commercial orchard injected with GA3 at 1.0 or 2.5.g per tree on 5 January (before bud break) started anthesis 3 and 23.d later than control trees, respectively. No determinate inflorescences were produced in any treatment. GA3 injections increased the proportion of inactive (quiescent) buds, resulting in fewer indeterminate inflorescences, but did not affect vegetative shoot number. The results of this research are the first to demonstrate that a high concentration of GA3 trunk-injected in the winter prior to bud break can, through increased bud abscission or inactivity, reduce inflorescence number, with no effect on vegetative shoot number. Yield reduction would be anticipated in response to trunk injection of 1.0.g GA3 per tree, because this treatment reduced both inflorescence number and fruit set/inflorescence. This, or a lower concentration, may prove useful in evening-out alternate bearing.

GA3 Application Alters Flowering Phenology of `Hass' Avocado

The objectives of the present research were to quantify 1) the contribution that vegetative shoots produced in the summer vs. fall and indeterminate vs. determinate inflorescences make to yield and 2) the effects of GA3 on flowering expression and inflorescence phenology of summer and fall shoots of `Hass' avocado (Persea americana Mill.) under field conditions. Anthesis started earlier on fall than summer shoots of 10-year-old `Hass' avocado trees; however, no difference in the date of full bloom was observed. Indeterminate inflorescences that underwent early anthesis set more fruit than those with delayed anthesis, conversely, determinate inflorescences with delayed anthesis set more fruit. Indeterminate inflorescences comprised 90% of total inflorescences and contributed 73% of total fruit yield, but individual determinate inflorescences were at least three times more productive than the indeterminate ones. Summer and fall shoots were sprayed with 0, 50, 100, or 1000 mg·L-1 GA3 in November, December or January. GA3 stimulated apical growth of all shoots. If secondary axes of an inflorescence bud were differentiated at the time of GA3 application, the inflorescence developed in advance of inflorescences on branches not treated with GA3. In addition, GA3 caused precocious development of the vegetative shoot of indeterminate inflorescences relative to the flowers in the same inflorescence and relative to the vegetative shoot of indeterminate inflorescences from untreated branches. Stimulation of vegetative growth at the inflorescence apex by GA3 inhibited growth of axillary buds. GA3 at 50 mg·L-1 had no effect on the number of determinate or indeterminate inflorescences produced by either summer or fall shoots. Higher concentrations of GA3 increased the number of vegetative shoots and inactive buds produced by both shoot types.

Inflorescence and Flower Development of the `Hass' Avocado (Persea americana Mill.) during “On” and “Off” Crop Years

Inflorescence and flower development of the `Hass' avocado (Persea americana Mill.) were investigated at the macro- and microscopic level with three objectives: 1) to determine the time of transition from vegetative to reproductive growth; 2) to develop a visual scale correlating external inflorescence and flower development with the time and pattern of organogenesis; and 3) to quantify the effect of high (“on”) and low (“off”) yields on the flowering process. Apical buds (or expanding inflorescences) borne on summer shoots were collected weekly from July to August during an “on” and “off” crop year. Collected samples were externally described and microscopically analyzed. The transition from vegetative to reproductive condition probably occurred from the end of July through August (end of shoot expansion). During this transition the primary axis meristem changed shape from convex to flat to convex. These events were followed by the initiation of additional bracts and their associated secondary axis inflorescence meristems. A period of dormancy was not a prerequisite for inflorescence development. Continued production of secondary axis inflorescence meristems was observed from August to October, followed by anthesis seven months later. In all, eleven visual stages of bud development were distinguished and correlated with organogenesis to create a scale that can be used to predict specific stages of inflorescence and flower development. Inflorescence development was correlated with minimum temperature ≤15 °C, whereas yield had little effect on the timing of developmental events of individual inflorescence buds. However, the high yield of the “on” year reduced inflorescence number and increased the number of vegetative shoots. No determinate inflorescences were produced during the “on” year. For the “off” year, 3% and 42% of shoots produced determinate and indeterminate inflorescences, respectively.

Characterization ofwaldmeister, a novel developmental mutant inArabidopsis thaliana

A novel Arabidopsis thaliana (L.) Heynh. developmental mutant, waldmeister (warn), is described. This mutant was found in the progeny arising from an Ac-Ds tagging experiment, but does not appear to be tagged by an introduced transposon. This recessive nuclear mutation maps between GAPB and ap 1 on chromosome 1 and shows extreme morphological and physiological changes in both floral and vegetative tissues. Changes to the vegetative phenotype include altered leaf morphology, multiple rosettes, stem fasciation, retarded senescence and disturbed geotropic growth. Changes to the floral phenotype include delayed flowering, increased number of inflorescences, determinate inflorescences, altered number and morphology of floral organs, chimeric floral organs, and ectopic ovules, warn was crossed to a number of previously described floral mutants: apetela 2, apetela 3, pistillata, agamous, and leafy. The phenotype of the double mutant was in each case additive. In the case of agamous, however, the indeterminate repetitive floral structure of agamous was lacking, emphasizing the determinate inflorescence growth of warn. The extreme phenotype of the warn mutant is suggestive of a disturbance to a gene of global importance in the regulation of plant growth and development.

Inflorescence morphology of <i>Lachiiaea</i> and <i>Cryptadenia</i> (Thymelaeaceae)

The current delimitation of Lachnaea L. and Cryptadenia Meisn. is based on the inflorescence morphology. In Lachnaea both indeterminate and determinate inflorescences occur, whereas in Cryptadenia only determinate inflorescences are present. The indeterminate inflorescences in Lachnaea are capitate or umbellate. The determinate inflorescences in both genera comprise a solitary, terminal flower. It is concluded that the two genera cannot be distinguished on inflorescence structure.

Two New Species of Cladocolea (Loranthaceae) from Mexico and Surinam

Cladocolea racemosa and C. elliptica are illustrated and described as new. The former, Mexican species is unique in the genus in having progressive indeterminate inflorescences, and highly unusual in having pedicellate flowers. The latter, Suriname species also has an indeterminate inflorescence, but is closely related to C. micrantha. Since my monograph of Cladocolea (Loranthaceae) (Kuijt, 1975), the circumscription of the genus has changed through the publication of new entities (Kuijt, 1981, 1987a, 1987b), the removal of some to the genus Ixocactus (Kuijt, 1991b), and the inclusion of species from the genus Phthirusa (Kuijt, 1991a). I originally visualized the genus as being characterized by determinate inflorescences, though even then a few clearly derived species had inflorescences that aborted terminally; and by flowers that were arranged in monads on inflorescences and were ebracteolate. The two new species violate both of these major generic characters: P. racemosa has a truly indeterminate inflorescence, and C. elliptica has at least some bracteolate triads at the base of an indeterminate inflorescence. In both cases, however, the alliances to the main body of Cladocolea seem beyond question, and these modified characters are regarded as derivative. Cladocolea racemosa Kuijt, sp. nov. TYPE: Mexico. Guerrero: 2.5 km al WNW de Tlaxco, camino de Tototepec a San Miguel Amoltepec, bosque de pino, ladera de exposici6n S. colgante parasito de Pinus, 2,100 m, 28 Mar. 1982, Lorea 1955 (holotype, FCME; isotypes, LEA, WIS). Figure 1. Plantae delicatissimae, graciles, pendulae, probabiliter dioeciae, solum masculae visae. Folia usque ad 60 x 4 mm, angustissime lanceolata. Inflorescentiae staminatae axillares, singulae, indeterminatae, racemosae, prophyllis binis crassis suffultae, floribus binis, pedicellatis, ebracteolatis 10-14; bractea suffulciens cum pedicello non coalita. Flores hexameri: petala staminaque dimorpha; antherae sessiles; sacculi polliniferi 4, connectivum in cornu prominens protractum. Extremely delicate and slender, glabrous plants, the leaf-bearing stems 1 mm or less thick, terete, sparsely branched, possibly sympodial. Leaves paired, to 6 cm long and 4 mm wide, very narrowly lanceolate, tapering into a slender petiole ca. 7 mm long, venation not evident except for the midrib, which runs into the apiculate apex. Probably dioecious, only the staminate seen. Inflorescence one per axil, indeterminate, subtended by two distinctive, thick, blunt, pink to purplish prophylls less than 0.5 mm long, and becoming at least 3-4 cm long in anthesis, racemose, bearing 10-14 paired, pedicellate flowers, the bracts 1 mm long, ovate, with rounded apex, caducous, completely free from the pedicels, which become 2.5 mm long and are deeply constricted just below the ovary in anthesis. Flower bud at least 5 mm long, one-third of which is an ovary with inconspicuous, smooth calyculus; petals 6, dimorphic, ca. 3 mm long; anthers 2 mm long, in 2 series, both series completely sessile, attached t the petal in the middle of the abaxial surface, a median ridge present below each anther; pollen sacs 4, the connective extended into a minute terminal horn; style 1.5 mm long, slender, straight, somewhat expanded just above the ovary, stigma poorly differentiated. This is perhaps the most anomalous species of Cladocolea, and it could be argued that a distinct genus should be erected for it. I prefer to maintain it in Cladocolea, even though this placement clashes with one major element of the current circumscription of the genus. This divergent feature is the progressive indeterminacy of the inflorescence. There exist several other species in the genus which, technically, also have indeterminate inflorescences, but the situation is different there in that all flowers mature more or less simultaneously, e.g., C. coriacea Kuijt (Kuijt, 1987a); C. cupulata Kuijt, C. mcvaughii Kuijt (Kuijt, 1975); C. biflora Kuijt (Kuijt, 1981). Considering that the terminal flower in most Cladocolea species tends to be the first to mature, the simultaneous maturation of all flowers may be seen as a transitional feature to true indeterminacy. In C. racemosa, progressive indetermiNOVON 2: 351-354. 1992. This content downloaded from 207.46.13.156 on Sat, 10 Sep 2016 04:03:34 UTC All use subject to http://about.jstor.org/terms

Inflorescence Structure and Generic Placement of Some Small-Flowered Species of Phthirusa (Loranthaceae)

Inflorescence structure is analyzed in three small-flowered species previously as- signed to Phthirusa, viz., P. micrantha, P. sandwithii, and P. myrsinites. The first two are characterized by determinate inflorescences, the terminal flower being followed by one or two pairs of (e)brac- teolate monads and, at least in P. micrantha, one or more pairs of bracteolate triads; occasionally in P. micrantha, plants have bracteolate monads only, but a terminal flower is always present. The result of this analysis is exclusion of the first two species from Phthirusa and their assignment to Cladocolea as C. micrantha comb. nov. and C. sandwithii comb. nov. In P. myrsinites, in contrast, the inflores- cence is an extremely condensed, indeterminate spike of bracteolate monads. The question of appropriate generic assignment of this species leads to a reconsideration of the status of the genus Maracanthus, which is synonymized to Oryctina. In consequence, I suggest that Oryctina be recon- stituted to consist of 0. scabrida, 0. subaphylla, 0. chlamydata comb. nov., 0. pedunculata comb. nov., 0. badilloi comb. nov., and 0. myrsinites comb. nov. Phthirusa savannarum is synonymized under the latter species.