Sexual systems in the New Zealand angiosperm flora

Figures & data

Table 1. Angiosperm sexual systems found in New Zealand angiosperms.

Flower level	Species level	Definition	Simplified category
Monoclinous, Perfect, Bisexual	Hermaphrodite	Each flower of each individual has stamens and pistils	Hermaphrodite (and Cosexual)
Diclinous, Imperfect, Unisexual	Gynomonoecious	Bisexual and pistillate flowers on same plant	Monoecious (and Cosexual)
	Andromonoecious	Bisexual and staminate flowers on same plant
	Monoecious	Unisexual flowers on the same plant.
	Dioecious	Each plant with only staminate or only pistillate flowers	Gender dimorphic
	Gynodioecious	Bisexual and pistillate flowers held on separate plants

Note: Complex variations of these systems occur when the idealised categories presented here blend into one another within a population. These are often referred to as polygamous systems or, in the case of dioecious plants where bisexual flowers occur sporadically, ‘leaky’.

Table 2. Life form classification for the New Zealand angiosperm flora (n = 2080 taxa) with the number of species of each gender in each lifeform.

			Cosexual				Gender dimorphic
Life form	Definition	No. species	H	M	GM	AM	GD	D
Woody	Significant lignification of above ground parts
Trees^1	Self-supporting but ≥5 m tall	237	123	9	4	1	24	77
Shrubs	Self-supporting and <5 m tall	382	206	3	23	0	77	72
Lianas^2	Climbers reliant on other plants for support	31	12	0	1	0	1	17
Herbaceous	No or insignificant lignification of above ground parts
Herbs^3	Self-supporting; includes sub-shrubs	1415	1026	156	67	28	33	105
Vines^2	Climbers reliant on other plants for support	15	12	3	0	0	0	0
All species		2080	1379	171	95	29	135	271

Note: H = hermaphrodite; M = monoecious; GM = gynomonoecious; AM = andromonoecious; GD = gynodioecious; D = dioecious.

¹ Height definitions of trees can range from 2–6 m, and some ignore height as a factor, defining shrubs as having numerous stems

² Vine is often used interchangeably with liana and the term climber often used without qualification

³ Sub-shrubs have herbaceous canopies but woody root stocks and lower stems

Table 3. Traits of New Zealand angiosperm genera with solely cosexual species or with at least one gender dimorphic species.

	Solely cosexual	Can be gender dimorphic
Number of genera	280	78
% all genera	78.2	21.8
% woody	22.8	62.8
% fleshy-fruited	17.2	50.0
% with biotic pollination	69.7	76.9

Note: Traits varied among species within genera and in this analysis, if any species in the genus was woody, fleshy-fruited, or had biotic pollination, the genus was considered to have that trait for this analysis.

Table 4. Distribution of plant sexual systems within traits and trait combinations in the New Zealand angiosperm flora.

Traits or trait combinations	Number of species	H	M	GM	AM	GD	D	Cosexual	Gender Dimorphic	χ^2	P
All species	2080	66.3	8.2	4.6	1.4	6.5	13.0	80.5	19.5
Woody + Fleshy + Abiotic Pollination	68	11.8	1.5	0.0	0.0	0.0	86.8	13.2	86.8	171.61	< 0.0001
Woody + Abiotic Pollination	77	11.7	7.8	0.0	0.0	0.0	80.5	19.5	80.5	159.06	< 0.0001
Fleshy-fruited + Abiotic Pollination	87	24.1	2.3	1.1	0.0	0.0	72.4	27.6	72.4	134.67	< 0.0001
Woody + Fleshy-fruited	278	26.6	2.5	0.0	0.0	23.4	47.5	29.1	70.9	336.96	< 0.0001
Fleshy-fruited	328	31.1	2.4	0.3	0.0	20.1	46.0	33.8	66.2	318.92	< 0.0001
Woody + Fleshy-fruited + Biotic Pollination	210	31.4	2.9	0.0	0.0	31.0	34.8	34.3	65.7	222.19	< 0.0001
Fleshy-fruited + Biotic Pollination	241	33.6	2.5	0.0	0.0	27.4	36.5	36.1	63.9	229.97	< 0.0001
Herbaceous + Fleshy-fruited + Biotic Pollination	31	48.4	0.0	0.0	0.0	3.2	48.4	48.4	51.6	17.72	< 0.0001
Woody	650	52.5	1.8	4.3	0.2	15.7	25.5	58.8	41.2	124.39	< 0.0001
Herbaceous + Fleshy-fruited	50	56.0	2.0	2.0	0.0	2.0	38.0	60.0	40.0	11.55	0.0007
Woody + Biotic Pollination	573	57.9	1.0	4.9	0.2	17.8	18.2	64.0	36.0	67.43	< 0.0001
Woody + Dry-fruited + Abiotic Pollination	9	11.1	55.6	0.0	0.0	0.0	33.3	66.7	33.3	0.39	0.5345
Biotic Pollination	1499	70.9	2.0	5.8	0.1	8.5	12.7	78.8	21.2	1.45	0.2289
Herbaceous + Fleshy-fruited + Abiotic Pollination	19	68.4	5.3	5.3	0.0	0.0	21.1	78.9	21.1	0.00	1.0000
Woody + Dry-fruited	372	71.8	1.3	7.5	0.3	9.9	9.1	80.9	19.1	0.02	0.9019
Woody + Dry-fruited + Biotic Pollination	363	73.3	0.0	7.7	0.3	10.2	8.5	81.3	18.7	0.08	0.7812
Abiotic Pollination	581	54.4	24.3	1.4	4.8	1.2	13.9	84.9	15.1	5.46	0.0195
Dry-fruited + Biotic Pollination	1258	78.1	1.9	6.9	0.1	4.9	8.1	87.0	13.0	22.81	< 0.0001
Herbaceous + Biotic Pollination	926	78.9	2.6	6.4	0.0	2.8	9.3	87.9	12.1	24.24	< 0.0001
Dry-fruited	1752	72.9	9.3	5.4	1.7	3.9	6.8	89.2	10.8	54.61	< 0.0001
Herbaceous + Dry-fruited + Biotic Pollination	895	80.0	2.7	6.6	0.0	2.8	7.9	89.3	10.7	33.87	< 0.0001
Herbaceous	1430	72.6	11.1	4.7	2.0	2.3	7.3	90.3	9.7	62.27	< 0.0001
Herbaceous + Dry-fruited	1380	73.2	11.4	4.8	2.0	2.3	6.2	91.4	8.6	76.81	< 0.0001
Herbaceous + Abiotic Pollination	504	60.9	26.8	1.6	5.6	1.4	3.8	94.8	5.2	59.06	< 0.0001
Dry-fruited + Abiotic Pollination	494	59.7	28.1	1.4	5.7	1.4	3.6	94.9	5.1	58.83	< 0.0001
Herbaceous + Dry-fruited + Abiotic Pollination	485	60.6	27.6	1.4	5.8	1.4	3.1	95.5	4.5	62.44	< 0.0001

Note: We present the number of species in the whole angiosperm flora (‘all species’) and in subsets of the whole flora according to one or more traits. We then give the percentage of those species in each of the six plant sexual systems (H = hermaphrodite; M = monoecious; GM = gynomonoecious; AM = andromonoecious; GD = gynodioecious; D = dioecious), followed by the sum of those percentage figures within cosexual and gender dimorphic species. The final two columns present results from χ² tests evaluating whether the distribution of cosexual and gender dimorphic species within a trait or trait combination group differs significantly from the overall distribution of cosexual and dimorphic species in the angiosperm flora (i.e. 80.5% cosexual and 19.5% gender dimorphic). Traits and trait combinations are sorted within the table in descending order of the prevalence of gender dimorphism.

Table 5. Gender dimorphism (dioecious + gynodioecious species) in the New Zealand angiosperm flora according to pairs of life history traits.

Level of comparison	Trait pair	Total	% gender dimorphism^1
Species	Herbaceous & abiotic pollination	504	5.2
	Herbaceous & biotic pollination	926	12.1
	Woody & abiotic pollination	77	80.5
	Woody & biotic pollination	573	36.0
Genus	Herbaceous & abiotic pollination	95	12.9
	Herbaceous & biotic pollination	160	11.2
	Woody & abiotic pollination	12	46.2
	Woody & biotic pollination	103	39.3

Note: Data are shown for species and genera. For genera comparisons, some genera are counted more than once because a genus was included in a trait pair if at least one species had that combination of woodiness and pollination mode.

¹ For species level comparisons, this is the % that are gender dimorphic; for genus level comparisons, this is the % of those genera that contain at least one gender dimorphic species

Figure 1. Frequency of the three major plant sexual systems within species that share combinations of woodiness, pollination mode, and possession of fleshy or dry fruits.

Table 6. Flower size (corolla diameter) in New Zealand biotically pollinated angiosperms (excluding Asteraceae and excluding abiotically pollinated species).

Flower size group	All sexes	Hermaphrodite	Monoecious^1	Gender Dimorphic^2	χ^2	P
All biotically	1202	877 (73%)	17 (1.4%)	308 (25.6%)	–	–
pollinated species
Small (0–4.9 mm)	320	170 (53.1%)	5 (1.6%)	145 (45.3%)	47.4	<0.0001
Medium (5–9.9 mm)	346	235 (67.9%)	7 (2.0%)	104 (30.1%)	3.58	0.1671
Large (10–14.9 mm)	202	168 (83.2%)	2 (1.0%)	32 (15.8%)	9.48	0.0087
Very large (≥15 mm)	334	304 (91.0%)	3 (0.9%)	27 (8.1%)	35.4	<0.0001

Note: Data are counts of species with percentages within rows given in parentheses. The final two columns present results from χ² tests evaluating whether the distribution of sexual systems within each flower size group differs significantly from the overall distribution of sexual systems in the whole biotically pollinated flora excluding Asteraceae (n = 1202 species).

¹ including andromonoecious & gynomonoecious

² dioecious and gynodioecious

Table 7. Flower colour and sexual system in New Zealand biotically pollinated angiosperms (including Asteraceae and excluding abiotically pollinated species).

Flower size group	All sexes	Hermaphrodite	Monoecious^1	Gender Dimorphic^2	χ^2	P
All biotically	1499	1063 (70.9%)	118 (7.9%)	318 (21.2%)	–	–
pollinated species
Green	186	114 (61.3%)	18 (9.7%)	54 (29.0%)	7.44	0.0242
Yellow	220	122 (55.5%)	50 (22.7%)	48 (21.8%)	50.0	<0.0001
White	884	666 (75.3%)	41 (4.6%)	177 (20.0%)	10.60	0.0050
Blue	80	73 (91.2%)	0 (0%)	7 (8.8%)	16.4	0.0003
Red	129	88 (68.2%)	9 (7.0%)	32 (24.8%)	0.96	0.6197

Note: Data are counts of species with percentages within rows given in parentheses. The final two columns present results from χ² tests evaluating whether the distribution of sexual systems within each flower colour group differs significantly from the overall distribution of sexual systems in the whole biotically pollinated flora including Asteraceae (n = 1499 species).

¹ including andromonoecious & gynomonoecious.

² dioecious and gynodioecious.

Figure 2. Sexual system versus height in the woody angiosperm flora of New Zealand.

Figure 3. Total basal area (m²) and stem count for all tree species sampled across 796 forest plots throughout New Zealand. D = gender dimorphic (n = 84 species sampled); H = hermaphrodite (n = 82 species sampled); M = monoecious (n = 12 species sampled).

Figure 4. Range sizes of New Zealand tree species, plotted by sexual system. Range size is the total number of 1° latitudinal bands where a species naturally occurs. Fitted linear models with 95% confidence intervals are shown for each sexual system.

Figure 5. Richness of New Zealand tree species in latitudinal bands by height class and sexual system.

Table 8. Genera in which it is probable that gender dimorphism evolved autochthonously in New Zealand.

Taxon	Gender types	Dimorphic/cosexual	Fruit type	Pollination syndrome	Life forms
Bulbinella	D, H	2/4	Dry	Biotic	Herb
Callitriche	D, M	1/3	Dry	Abiotic	Herb
Chionochloa	GD, H	1/23	Dry	Abiotic	Herb
Gentianella	GD H	1/29	Dry	Biotic	Herb
Coprosma	D, H	54/1	Fleshy	Abiotic	Tree, shrub
Lepidium	D, H	2/18	Dry	Biotic	Shrub, herb
Leptinella	D, GD, M	10/15	Dry	Biotic	Herb
Leucopogon	D, H	1/4	Fleshy	Biotic	Tree, shrub
Mentha	GD	1/0	Dry	Biotic	Herb
Pachycladon	GD, H	4/10	Dry	Biotic	Herb
Ranunculus	GD, H	1/44	Dry	Biotic	Herb
Toronia	D	1/0	Fleshy	Biotic	Tree
Urtica	D, M	2/3	Dry	Abiotic	Shrub, herb, vine
Veronica	D, GD, H	34/126	Dry	Biotic	Tree, shrub, herb

Note: Traits (fruit type, pollination syndrome, life form) apply only to New Zealand representatives. Gender types: D = dioecious; GD = gynodioecious; M = Monoecious; H = Hermaphrodite.

Table 9. Incidence of the three major plant sexual systems in a selection of global angiosperm floras.

Location	References	N species	% trees	% woody	% hermaphrodite	% monoecious^1	% gender dimorphic^2
Carolinas, USA	Conn et al. (1980)	3274	12.1	25.9	–	–	3.5
British Isles	McComb (1966), Kay and Stevens (1986)	1377	3.8	–	80.7	16.3	3.7
Wisconsin, USA	Givnish et al. (2020)	1547	3.7	13.7	73.9	18.9	4.7
Changbai Mountain, China	Xia et al. (2020)	1403	5.1	17.5	81.6	13.3	5.1
Puerto Rico & Virgin Islands	Flores and Schemske (1984)	2027	22.7	50.8	78.9	14.9	6.1
Sri Lanka	Senarath (2008)	3529	21.9	48.8	82.7	10.3	7.1
Venezuela, Central Plain	Ramírez (2005)	210	14.3	26.7	75.2	17.1	7.6
Canadian Arctic	Kevan and Godglick (2016)	355	1.1	8.7	–	–	7.9
Taiwan	Lin et al. (2020)	3484	14.9	37.5	73.1	10.7	8.1
Chamela, Mexico	Bullock (1985)	708	26.6	49.9	70.2	16.9	13
Restinga, Brazil	Matallana et al. (2005)	566	18.7	43.2	75	11	14
Hawai'i	Sakai et al. (1995a)	971	26.8	65.1	62.4	16.0	18.5
New Zealand	This work	2080	11.4	31.3	66.3	14.2	19.5
Singapore	Sodhi et al. (2008)	1882	42.5	64.2	69.4	10.3	20.3
New Caledonia	Schlessman et al. (2014)	3051	46.7	76.0	61.2	17.5	21.2
Xishuangbanna, China^3	Chen and Li (2008)	685	57.5	88.7	60.6	14.3	25.1

¹ including andromonoecious & gynomonoecious.

² dioecious and gynodioecious.

³ forest only.

Figure 6. Key examples of sexual systems in New Zealand angiosperms. A, Myrsine salicina (Myrsinaceae). Gender dimorphism is rich among fleshy-fruited, subcanopy tree species. B, Aciphylla colensoi (Apiaceae). Gender dimorphism in herbaceous species is strongly concentrated in two genera, namely Aciphylla and Astelia. C, Astelia fragrans (Asteliaceae). D, Fuscospora cliffortioides (Nothofagaceae). Monoecy is uncommon in New Zealand woody plants, but is found in the five species of Nothofagaceae that dominate forest structure (48.4% of basal area nationally). E, Ascarina lucida (Chloranthaceae) is a rare example of a small monoecious tree. F, Carex decurtata (Cyperaceae). Monoecy is found in just 296 species but 66.7% of those are species of Carex. G, Pterophylla racemosa (Cunoniaceae) and H, Beilschmiedia tawa (Lauraceae). Tall and dominant forest species tend to be cosexual, and these two species contribute 20% of basal area nationally.

Figure 7. Percent gender dimorphism in the flora versus percent tree species in the flora, for 16 floras. The three Pacific archipelagos with high gender dimorphism (New Zealand, New Caledonia, and Hawai'i) are shown. Fitted linear model with 95% confidence intervals excludes New Zealand because it is an apparent outlier (%) flora ∼ 2.91 + (0.384 × % trees); F­_1,13 = 57.1, P < 0.0001, adjusted R² = 0.84. Data and data sources are provided in Table 3.

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Data availability

A full copy of the data are available from the Manaaki Whenua – Landcare Research Datastore website: https://doi.org/10.7931/qzf7-9q70.