r9901 NAUMAN: INTERGENERICHYBRIDIZATION Principes,34(4), 1990, pp. l9l-198 lntergeneric Hybridization between Coccothrinax and Thrinax (Palmae:Coryphoideae) CrmroN E. NeulreN Fairchild Tropical Garden, lO9Ol Old Cutler Road, Miami, Florid.a 33156t Assrnecr assertionthat the plants representan inter- generic hybrid betweenthese two species. Unusual plants of what initially appeared to be a species of Thrinax were discovered in the Lower Hybrids among vascular plants are suf- Florida Keys. The plants were observed to produce ficiently well known that several criteria abundant inflorescences,but anthesis and fruit set can be used to establish a hybrid origin. did not occur. The sterility, apparent intermediate- Among these,the most important criterion ness in several leaf characters, and consistent co- is that the putative hybrid occurrencewith Coccothrinax argentata (Jacq.) Bai- exhibits mor- ley and Thrinax morrisii H. A. Wendl. suggesteda phological intermediateness between its hybrid, Three criteria were evaluated to test the parents, usually in several characters. hypothesis of hybridity: morphological intermediate. Seven additional criteria were listed by ness, occurrence in the geographical zone of overlap Gottlieb (1972\. Since Gottlieb was con- of the putative parent species, and occurrence in ecologically intermediate habitats. Fifteen of the 22 cerned primarily with the confidence of characters examined exhibited intermediateness, three detecting a hybrid origin for stable, pre- exhibited questionable intermediateness, and five sumably reproducing entities, and since exhibited apparent heterosis. Field studies indicated these plants do not produce functional the putative hybrids to occur only with both parental flowersothree of these criteria cannot speciesand only where the parents occur in immediate be proximity to each other in ecologically intermediate appliedto the presentstudy. These are the habitats. presence of partial F, fertility, the pres- ence of unusual amounts of interpopula- Unusualplants of what initially appeared tional variability in the hybrid, and occur- tobe Thrinax morrisii H. A. Wendl. were rence in more recent geologicalformations discoveredby a local naturalist (Ann Wil- than the parent species.The relatively long liams) on No Name Key, Florida. The generationtime in Coccothrinax and Thri- plants were subsequentlyfound in several nax, and the logistic difficulties of crosses additional locations on neighboring Big Pine for experimental synthesis of the hybrid Key (Fig. I). During several years of (Read 1975), are sufficiently prohibitive observation,none of theseplants produced that this criterion cannot be evaluated.An flowers, but abortive inflorescenceswere additive chemicalprofile for marker paren- produced in abundance. This production tal compounds is also typical of hybrids of abortive inflorescencesand an apparent but is here consideredessentially equiva- intermediatenessand co-occurrence with lent to morphologicalintermediateness for' Coccothrinax argentata (Jacq.) Bailey practical comparisons.Other criteria relat- (fig. 2) and T. morrisii (Fig. 3) led to the ing to polyploid hybrids, e.g., chromosome number, pairing behavior, etc., could not I Present address:30I Hesler Biology Bldg., Univ. be applied. Previous chromosome counts of Tennessee.Knoxville. TN 37996-I I I0. of T. morrisii and of C. argentata (Read. r92 PRINCIPES lvor. 34 at the herbarium of Fairchild Tropical Gar- den (FTG). Results Intermediatenessand apparent hetero- sis is indicated for all of the characters of gross morphology examined. The scatter diagram (Fig. 4) illustrates severalofthese intermediate characters. Other characters showing this pattern include: presenceor absenceoftransverse veins, segmentshape ratio (distance to widest point along the segment,/segmentwidth), greater palman length (distance from the hastula to the sinus between the two central segments), degree of segment splitting, frequency of split petiole bases,and shapesofthe adax- ial and abaxial hastulas. The ranges of character state expressionin three char- acters, lamina outline, lamina folding, and segment habit are considerable,and dif- l. Habit of the putative hybrid ferences are in the form of frequenciesof characterstates. Heterosis is indicated for five charac- 1963, 1964, 1965, I97 S;Venl<atasubban ters: petiole apex width, adaxial hastula I945) report n : lB and a relativelyuni length, central segmentlength, lesser pal- form karyotype. This is apparentlythe case man length (distance from the hastula to for most Coryphoidpalms (Reail 1965). A the sinusesbetween segmentsadjacent to polyploid origin is therefore unlikely. the central segments),and distance to the point of maximum segment width. How- Materialsand Methods ever, the heterosisis mostly statistical and Morphologicalintermediateness was strongly indicated only for adaxial hastula tested by selecting 22 charactersthought length and segment length. For the other to differ betweenthe parentalspecies (Table heterotic characters the intermediate's I ). Characterstates were recorded for pop- range of expressionis entirely within the ulations of the parental species and the range of expressionexhibited by T. mor- putative hybrid from Big Pine Key, Mon- risii (Table I). roe County, Florida. Two fully expanded, All three anatomical characters (20- apparentlyhealthy leavesnot showingsigns 22,Table l, Fig. 5) showedintermediate- of senescencewere randomly selectedfrom ness. Small, abaxial fiber bundles in C. mature plants (i.e., plants with at least one drgentata are contained entirely within inflorescenceat any stageofdevelopment). the hypodermis. In Z m,orrisii these bun- For leaf anatomy characters,a rectangular dles only occasionallyinterrupt the hypo- sampleof lamina tissuemeasuring 2-3 cm dermis. The bundlesin the putative hybrid on a side was removed after drying. The interrupt, but are not contained entirely sampleswere rewetted for several days in within the hypodermis. Thrinax tnonisii 5% NaOH and stained with basic fuchsin is characterizedby a mesophyll consisting for cross sections.Vouchers are deposited almost entirely of palisade cells and C. 19901 NAUMAN: INTERGENERICHYBRID 2. Habit of Coccothrinax argentata. 3. Habit oI Thrinax morrisii. argentata by a mesophyll of both palisade mer location on No Name Kev (Monroe and spongy mesophyll cells. The putative Co., Florida). The putative hybrids only hybrid exhibits a mesophyll of largely pal- occur in mixed populationsof C. argentata isadecells and a more or lessdistinct spongy and T. morrisil, and in all casesless than Iayer. Fibers surrounding secondary veins five meters from plants of both parental in C. argentata extend from the abaxial species.The putative hybrids are not known to the adaxial epidermis, interrupting the from areas or habitats occupied by only hypodermis both abaxially and adaxially. one of the parental species. The mixed In T. morrisii, these same fibers rarely nature of the parental populations can be extend acrossthe entire width of the meso- taken as evidence of ecological interme- phyll and generally do not interrupt the diateness.Coccothrinax argentata occurs hypodermis. The putative hybrid exhibits in coastal pinelands or strand habitats in a condition closer to that seenin C. argen- the lower Florida Keys and along the east- tata,bul the fibers generally do not inter- ern coast from southern Dade Countv. rupt the hypodermis. Florida, north to Lake Worth in Palm Field studies verified the putative Beach County (Fig. 6). Thrinax rnorrisii hybrid's occurrence in the geographical occurs in wooded areas, hammock edges range of overlap and in habitats ecologi- and in mangrove and tropical strand hab- cally intermediate between the parental itats from Key Largo southward (Fig. 6). species.Hybrids are known from22loca- Coccothrinaxargentata co-occurswith I tions on Big Pine Key, and from one for- morrisii only in the slash pine flatwoods t94 PRINCIPES [Vor. 34 Table 1. Means and rdnges of expressionin characters examined/or Coccothrinax argentata, Thrinax morrisii, and their putatiae hybrid. ("mostly" meansmore than 807o "f ,tt" t"-tt"+ Character C. argentata Hybrid T. morrisii 1. Petiole base split no mostly yes, rarely no yes 2. Petiole apex width 1.40(0.9-r.9) r.72(r.2-2.0) r.47 (0.6-2.0) (cm) 3. Abaxial hastula straight to broad-round- straight to obtuse-round- rounded, deltoid apical shape ed, apical tooth pres- ed, apical tooth pres- tooth mostly absent ent or absent ent or absent 4. Adaxial hastula obtuse to rounded trian- obtuse to acute rounded, obtuse rounded, apical shape gular, apical tooth apical tooth present tooth mostly absent present 5. Adaxial hastula 0.6 (0.5 0.8) r.2(r.0-r.s) 0.7(0.s-0.9) length (cm) 6. Abaxial lamina indu- dense moderate scattered & few ment density 7. Wax dots present absent few to absent presenr B. Transverse veinlets absent obscure but present obvious 9. Segment number 3s.0 (29-42) 44.4 (39-48) 49.2(4s-s6) 10. Lamina outline 3/+to )I orbicular Yr to )1 orbicular I to >1 orbicular Il. Lamina form flat or with I raised mostly with several mostlymore than I group of segments groups of raised seg- groupof raisedseg- menTs ments 12. Segment habit arching to mostly droop- mostly drooping or arch- straightto arching ing or pendent ing-pendent 13. Central segment 5.72 (s.2 6.4) 8.r8(7.s-9.0) 6.77(6.0-7.9) length (dm) 14. Central segment 2.34(2.r-2.6) 3.52(3.0-3.7) 3.93(3.s-4.6) maximum width (cm) 15. Distanceof maxi- 2.06 (1.7s-2.23) 3.49(2.92-4.4s) 3.34(2.89-4.08) mum segment width from hastula (dm) 16. Shaperatio charac- 2.80 (2.37-3.20) 2.4(1.68-2.93) 2.04(r.9r-2.38) ter I3./character 15 17. Greaterpalman r.i3 (0.80 r.91) 2.97(2.67-3.s4) 3.06(2.75-3.68) length (dm) 18. Lesserpalman 1.07(0.52-1.8?) 2.8(2.34-3.37) 2.74(2.49-3.26) length (dm), second sinus either side of the central segments 19. Degree of splitting 16.68(r0.8-36.9) 39.22(33.0-51.6) 4s.r (40.7-47.2) character 17 x 100,/characterl3 20. Abaxial fiber bundle bundles contained entire- bundles not contained bundlesoccasionally in- intrusion into the ly within the hypoder- within, but interrupt- terruptingthe hypo- hypodermis mis ing the hlpodermis dermis 2I.