Many African (incl. Madagascan) Podostemaceae have ribbon-like or foliose roots, erect or inverted flowers in the bud stage (spathella), 1-locular or 2-locular ovaries, pollen in monads or dyads (Ameka et al. 2002, 2003). The multiple-access key does not help when only such character-states are observable. This key is also useless as long as the plant has a standard set of characters such as two stamens with common stalk (andropodium), or capsules valves with three ribs, each extending from base to apex. However, it may be helpful when unusual or unique characters are observable, restricted to a small number of taxa. They will be mentioned below. Characters I – VIII focus on morphological peculiarities of the vegetative body (roots, stems, leaves, scales) as well as flower position; characters IX – XVII cover unique features of the flowers and fruits.

I. Stems lacking, all leaves and flower buds sessile, inserted on upper surface of foliose (crustaceous) root. The following list contains some (but probably not all) taxa with this pattern (see footnote 1):
- Ledermanniella aloides, L. thalloidea [Angola, Cameroon, SierraLeone]: capsules ellipsoidal, not compressed; stems may be present (usually short in L. aloides)
- Macropodiella pellucida [Cameroon]: capsules laterally compressed; stems seem to lack completely in this species!
- Sphaerothylax abyssinica [Ethiopia, Kenya, Tanzania, Malawi, Zimbabwe, Madagascar]: capsules globose to subglobose, not compressed; stems may be present
- Stonesia heterospathella [Guinea, Sierra Leone]: capsules broadly ellipsoidal, slightly compressed, with peculiar rib pattern!

II. Scales, 0.5 – 2 (rarely up to 5) mm long, around the stems, arranged irregularly or in more than two rows; often overlapping each other and covering the surface of certain stem portions completely; scales may be triangular, orbicular or even linear; they are arranged irregularly or in three rows:
- Tristicha trifaria [many African countries and Madagacar]: scales ovate to narrow lanceolate, often with midrib; in three rows along moss-like photosynthetic branchlets (“ramuli”)
- Ledermanniella subg. Phyllosoma [20 spp., W, SW and Central tropical Africa]: scales entire or dentate to lobate, never with midrib; arranged irregularly along stems, never in three rows; large compound leaves (> 2 cm long, forked into linear segments) usually present as well; see KEY F AND KEY G!

III. Peculiar leaf shape: lanceolate to ribbon-like blades with more than 4 parallel nerves (ribs)
- Ledermanniella letouzeyi [Cameroon]: prominent leaves (up to 30 cm long), entire and narrow lanceolate (width up to 2 cm) or bifurcated once or twice into narrow lanceolate segments (width up to 2 cm) (see footnote 2)
- Thelethylax minutiflora [Madagascar]: certain forms (especially Perrier’s subsp. orientalis) with entire elliptical to oblong blade, 3-4 cm long and 7-17mm wide

IV. Peculiar leaf sheaths, presence of intrapetiolar stipules; most African Podostemoideae have leaf sheaths with two attached lateral stipules or without any type of stipule!

- Ledermanniella bowlingii [Ghana], L. prasina [Cameroon], L. thalloidea [Cameroon]: especially bracts (leaves just below flowers or flower clusters) with hood-like sheath (see footnote 3) and dorsally inserted blade which is thread-like or forked once

V. Stems with secund inflorescences; i.e. reproductive shoots with elongate stems and flowers or (stalked) flower clusters restricted to one stem sector, occasionally flowers or flower clusters opposite to leaves which are restricted to another stem sector:
- Dicraeanthus africanus [Cameroon]
- Ledermanniella subg. Ledermanniella: L. boloensis, L. nicolasii [both Gabon]
- Leiothylax callewaertii [Zaïre]
- Macropodiella hallaei, M. heteromorpha, M. taylorii, M. uoroensis [Equatorial Guinea, Gabon, Cameroon, Ivory Coast]

VI. Stems with solitary flowers (or flower clusters) arranged in two rows (orthostichies), i.e. in the same plane as the distichously inserted foliage leaves. Exceptions as follows:

- Ledermanniella annithomae [Cameroon, Gabon]: each flower (or cluster) opposite a foliage leaf
- Stonesia taylorii [Guinea, close to Mali]: flowers usually along two rows; only one row of flowers (i.e. 1-flowered short-shoots) well developed; flowers of second row stay rudimentary; thus inflorescence seemingly secund

VII. Terminal flowers or terminal flower clusters, arising from angles of repeatedly forked stems or from angles of repeatedly forked leaf blades; i.e. shoot and its subunits with repetition of Y-shaped branching and flower(s) in between:
- Ledermanniella letouzeyi [Cameroon]: few flowers epiphyllous in angles of forked leaf blades, most flowers along stem (see footnote 4)
- Ledermanniella letestui [Gabon], L. prasina (see footnote 5) [Cameroon], L. schlechteri [Cameroon, Congo, Zaïre]
- Macropodiella garrettii (see footnote 6) [Sierra Leone]

VIII. Terminal leaves (see footnote 7) ; foliage leaves arise from the distal angles of repeatedly forked stems. They may be called „terminal leaves“ because they terminate the mother stem and give rise to two daughter stems which form the legs of the new stem fork (see Ameka et al. 2003; Rutishauser 2004).
- Ledermanniella bowlingii (subg. Ledermanniella) [Ghana]
- Ledermanniella abbayesii, L. adamesii (subg. Phyllosoma) [Guinea, Sierra Leone]
- Terminal leaves may also occur in other African Podostemoideae, at least occasionally (see e.g. Ledermanniella tenax, Cusset 1997, Fig. 1-B1; Zehnderia, Cusset 1987: Fig. 16-1).

IX. Spathella lacking; i.e. no tubular or saccate thin cover around the flower bud:
- Tristicha trifaria (because this is the only tristichoid member in Africa and Madagascar!)

X. Unusual orientation of flower buds in spathella; most African (Madagascan) members of subfamily Podostemoideae have flowers which are erect or completely inverted in the spathella. Exceptions as follows:
- Djinga felicis [Cameroon], Letestuella tisserantii [Western to Southern Africa]: flowers often not erect, but slightly inclined (oblique) in the spathella; i.e. the longitudinal axis of the ovary forms a right or obtuse angle as compared to the longitudinal axis of the spathella
- Thelethylax isalensis [Madagascar]: flowers strongly inclined or inverted in the spathella

XI. Three subulate (inconspicuous) tepals (see footnote 8) per flower, associated with 2 stamens with common stalk (andropodium); one tepal on each side of the andropodium, the third tepal in the fork between the filaments:
- Stonesia spp. (all species) [tropical W Africa]
- Thelethylax minutiflora, Th. isalensis [Madagascar]

XII. Increased stamen number per flower, usually with common stalk (andropodium).
Typical flowers of African and Madagascan Podostemoideae have Y-shaped structure with only 2 stamens on a common stalk (= andropodium) or just 1 stamen. Exceptions as follows:

• Stamens 2 and 3 (usually on the same individual):
- Ledermanniella subg. Ledermanniella: L. boloensis, L. raynaliorum, L. sanagaensis, L. variabilis (the latter species with up to 4 stamens) [Gabon, Cameroon, Nigeria]
- Ledermanniella subg. Phyllosoma: L. annithomae, L. harrisii [Gabon, Cameroon, Sierra Leone]
- Leiothylax quangensis [Cameroon, Zaïre]
- Macropodiella hallaei, M. heteromorpha, M. taylorii, M. uoroensis [Equatorial Guinea, Gabon, Cameroon, Ivory Coast]
- Winklerella dichotoma [Cameroon]
- Zehnderia microgyna [Cameroon]

• Stamens 3 or 4 (on the same individual):
- Angolaea fluitans [Angola]
- Ledermanniella variabilis (this species also with 2 stamens, see above) [Cameroon]

XIII. Unusual length proportions of common stalk (andropodium) to free filaments; when there are 2 (or 3 or 4) stamens per flower in African Podostemoideae the filaments have about the same lengths as the common base (andropodium); exceptions as follows:

• Filaments very short, less than ½ of anther length, andropodium much longer
- Ledermanniella bifurcata [Cameroon, Congo, Gabon], L. letestui [Gabon], L. torrei [Mozambique]
- Letestuella tisserantii [Western to Southern Africa]

• Filaments usually much longer than anthers and andropodium
- Angolaea fluitans [Angola]: the 3 (rarely 4) stamens free or united only at the base (i.e. with very short andropodium
- Ledermanniella variabilis [Cameroon]: the 2 – 3 (or rarely 4) stamens usually with short andropodium

XIV. Stigma shape, as observable in open flowers. Usually there are two stigmas (stigma lobes) which are linear or short. Exceptions as follows:

• Semi-globose stigma on a single style
- Angolaea fluitans [Angola]

• Two stigmas conical, rigid, erect and parallel
- Dicraeanthus africanus, D. zehnderi [Cameroon]
- Ledermanniella bowlingii, with the two erect stigmas fused into one basal cushion [Ghana]

• Two stigmas linear, each stigma with bifid apex
- Ledermanniella prasina [Cameroon]

• Two stigmas cock’s comb-like with serrate margin
- Macropodiella heteromorpha [Gabon, Cameroon, Ivory Coast]

• Three linear stigmas
- Tristicha trifaria

XV. Capsule stalk and gynophore (ovary stalk). Unlike most American and Asian members of the family, the ovaries and capsules of African Podostemoideae often show a stalk = gynophore (up to 1 mm, usually shorter than the mature capsule). Moreover, African Podostemoideae have a flower stalk (pedicel, i.e. the stalk below the insertion of the androecium) of 3 – 10 mm length. Exceptions as follows (measured when capsules mature):

• Pedicels up to 15 or more mm, gynophores up to 8 mm
- Zehnderia microgyna [Cameroon]: capsules subglobose, smooth
- Dicraeanthus africanus [Cameroon]: capsules cylindrical, ribbed (see footnote 9)
- Leithylax callewaertii, L. quangensis [Cameroon, Zaïre]: capsules globose, ribbed

• Pedicels and gynophores lacking or nearly so (thus, capsules subsessile within spathella)
- Saxicolella amicorum, S. submersum [Ghana]; pedicels up to 2 mm in Saxicolella spp.

XVI. Capsule shape; apex of capsule (ovary) with teeth or horns. Typical capsules are globose to ovoid or fusiform (spindle-shaped), i.e. with circular cross-section. All examples mentioned below have (as typical for African Podostemoideae) three ribs per valve, each extending from base to apex. They are exceptional with respect to their capsule shape:

• Capsules strongly flattened, with two flattened apical horns; i.e. similar to Veronica capsules:
- Winklerella dichotoma [Cameroon]

• Capsules slightly to strongly flattened, but without apical teeth or horns
- Macropodiella spp., only slightly flattened capsules in M. taylorii [tropical W Africa incl. Equatorial Guinea]
- Thelethylax spp. [Madagascar]

• Capsules slightly flattened, with two apical teeth (i.e. conspicuous tips of the two median ribs)
- Ledermanniella congolana [Zaïre]

• Capsules spindle-shaped, not flattened, with six apical teeth (i.e. conspicuous tips of six ribs)
- Ledermanniella warmingiana [Angola, Namibia]

XVII. Increased rib number per capsule valve (i.e. more than 3 ribs per valve), with the ribs nearest the sutures shorter than the others and not reaching the ends of the valves

- Stonesia spp. [Guinea, Sierra Leone], all with broadly ellipsoidal capsules, each valve with 5 or 7 ribs (i.e. with 12 or 16 per capsule)
- Endocaulos mangorense [Madagascar], capsule asymmetrically ovoid and slightly flattened, each valve with 7 ribs
- Paleodicraeia imbricata [Madagascar], capsule ovoid and slightly flattened, each valve with 5 ribs (see footnote 10)

Footnotes

1 There must be other podostemoid taxa in Africa with this habit when elongate shoots are lacking or already dropped.

2 See description and figures in Rutishauser (2004); check also if Macropodiella pellucida (usually devoid of stems and prominent leaves at all) rarely produces "de grandes lames foliacées plurinervées" (as mentioned by Cusset 1987:64)

3 This hood-like or scale-like sheath is homologous to an intrapetiolar (median) stipule (see Ameka et al. 2003).

4 See Rutishauser (2004): L. letouzeyi with epiphyllous flowers inserted in angles of forked leaf blade

5 See Schenk & Thomas (2004): flowers perhaps also epiphyllous in angles of forked leaf blades (?)

6 See Cusset (1978, Fig. 4-1)

7 Terminal leaves (with two opposite sheaths!) are found in many American Podostemoideae. (see Rutishauser 1995, 1997).

8 Tristicha trifaria (subfamily Tristichoideae) has also 3 tepals; unlike all African Podostemoideae the Tristicha tepals are conspicuous, forming a complete (imbricate) cover around the inner flower parts.

9 Check Hess (1961): Dicraeanthus africanus with capsule stalks up to 6 cm (!)

10 Verify this rib pattern in Paleodicraeia , see Cusset 1972, Fig.2-4; check also Thelethylax , the third podostemoid genus of Madagascar, having 3 ribs per valve, perhaps the two lateral ones also not reaching the ends of the valves (see Cusset 1972, Fig.3-4, especially T. isalensis )